Add GitHub Actions workflows for Linux, macOS, and Windows builds

This commit introduces three new GitHub Actions workflow files to automate
the compilation of the Telegram Desktop application on Linux, macOS, and
Windows platforms.

- `.github/workflows/build-linux.yml`: Defines the Linux build process,
  leveraging the existing Docker setup for dependency management and compilation.
- `.github/workflows/build-macos.yml`: Defines the macOS build process,
  including steps for dependency preparation using `prepare.py`, caching,
  and building via CMake.
- `.github/workflows/build-windows.yml`: Defines the Windows build process,
  similarly using `prepare.py` for dependencies, caching, and MSVC/CMake
  for compilation.

The workflows are designed to compile the application and upload the resulting
binaries as artifacts. They attempt to use existing build scripts and tools
from the repository where possible. Adjustments have been made based on analysis
of scripts like `prepare.py` and `qt_version.py` to correctly set environment
variables (e.g., QT versions).

A potential issue not fully resolvable without live testing is the dependency
on a `DesktopPrivate` repository, which is checked in some build scripts.
If this is essential for basic compilation, the workflows might require further
adjustments or access to this private repository.

.github/workflows/build-linux.yml

@@ -0,0 +1,77 @@
+name: Build Linux
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        submodules: 'recursive' # Important if ThirdParty libs are submodules
+
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v2
+
+    - name: Cache Docker layers
+      uses: actions/cache@v3
+      with:
+        path: /tmp/.buildx-cache
+        key: ${{ runner.os }}-buildx-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-buildx-
+
+    - name: Login to GitHub Container Registry
+      uses: docker/login-action@v2
+      with:
+        registry: ghcr.io
+        username: ${{ github.repository_owner }}
+        password: ${{ secrets.GITHUB_TOKEN }} # GITHUB_TOKEN is automatically created
+
+    - name: Build and push Docker image
+      uses: docker/build-push-action@v4
+      with:
+        context: ./Telegram/build/docker/centos_env
+        file: ./Telegram/build/docker/centos_env/Dockerfile # Assuming Dockerfile is here
+        push: false # Set to true if you want to push to ghcr.io
+        tags: ghcr.io/${{ github.repository_owner }}/tdesktop-centos-env:latest # Example tag
+        cache-from: type=local,src=/tmp/.buildx-cache
+        cache-to: type=local,dest=/tmp/.buildx-cache-new,mode=max
+        # build-args: | # If Dockerfile needs build args
+        #   SOME_ARG=value
+
+    # This step will be executed after the image is built and (optionally) pushed
+    - name: Move Docker cache
+      run: |
+        rm -rf /tmp/.buildx-cache
+        mv /tmp/.buildx-cache-new /tmp/.buildx-cache
+
+    - name: Run build script in Docker container
+      run: |
+        docker run --rm \
+          -v ${{ github.workspace }}:/usr/src/tdesktop \
+          ghcr.io/${{ github.repository_owner }}/tdesktop-centos-env:latest \
+          /usr/src/tdesktop/Telegram/build/docker/build.sh
+      # Note: The above docker run command assumes build.sh is executable
+      # and all necessary paths inside the container are correct.
+      # It also assumes that build.sh places artifacts in a subdirectory
+      # of ${{ github.workspace }}/Telegram/../out/Release (e.g., /usr/src/tdesktop/out/Release)
+
+    - name: Upload Telegram binary
+      uses: actions/upload-artifact@v3
+      with:
+        name: Telegram-linux
+        path: ${{ github.workspace }}/out/Release/Telegram # Adjust path if necessary
+        if-no-files-found: error
+
+    - name: Upload Updater binary
+      uses: actions/upload-artifact@v3
+      with:
+        name: Updater-linux
+        path: ${{ github.workspace }}/out/Release/Updater # Adjust path if necessary
+        if-no-files-found: error

.github/workflows/build-macos.yml

@@ -0,0 +1,74 @@
+name: Build macOS
+
+on:
+  push:
+    branches: [ master, main ]
+  pull_request:
+    branches: [ master, main ]
+
+jobs:
+  build:
+    runs-on: macos-12 # Using macos-12 for now, might need adjustment based on Xcode/SDK requirements
+    env:
+      MACOSX_DEPLOYMENT_TARGET: "10.13" # As seen in prepare.py
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        submodules: 'recursive'
+
+    - name: Select Xcode version (if specific version needed)
+      run: sudo xcode-select -s /Applications/Xcode_13.4.1.app/Contents/Developer # Example, adjust as needed
+
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.x' # prepare.py uses python3
+
+    - name: Cache Dependencies
+      id: cache-deps
+      uses: actions/cache@v3
+      with:
+        path: |
+          ${{ github.workspace }}/Libraries
+          ${{ github.workspace }}/ThirdParty
+        key: ${{ runner.os }}-deps-${{ hashFiles('Telegram/build/prepare/prepare.py', 'Telegram/build/qt_version.py') }}
+        restore-keys: |
+          ${{ runner.os }}-deps-
+
+    - name: Install Python dependencies for prepare.py (if any)
+      run: |
+        # Assuming prepare.py and its direct imports don't have external pip dependencies
+        # If they do, they should be installed here.
+        echo "No Python dependencies to install for prepare.py itself for now."
+
+    - name: Run prepare.py for dependencies
+      if: steps.cache-deps.outputs.cache-hit != 'true'
+      run: |
+        cd Telegram/build/prepare
+        python3 prepare.py skip-release # Adding skip-release as we only want to compile
+        # prepare.py will build into Libraries and ThirdParty folders at the repo root.
+      env:
+        QT: '5.15.2' # Example, this should ideally be determined by qt_version.py logic if possible
+                     # or made a matrix variable if multiple Qt versions need support.
+
+    - name: Configure build (emulating build.sh steps)
+      run: |
+        cd Telegram # build.sh runs configure.sh from Telegram directory
+        # Forcing specific architectures for CI; can be parameterized or matrix later
+        # Using x86_64 for macos-12 runner for broader compatibility for now
+        ./configure.sh -D DESKTOP_APP_MAC_ARCH="x86_64" -D DESKTOP_APP_DISABLE_JEMALLOC=ON
+        # DESKTOP_APP_DISABLE_JEMALLOC=ON is often useful for CI/dev builds
+
+    - name: Build Telegram
+      run: |
+        cd out # configure.sh creates an 'out' directory at the repo root
+        cmake --build . --config Release --target Telegram -j $(sysctl -n hw.ncpu)
+
+    - name: Upload Telegram.app
+      uses: actions/upload-artifact@v4
+      with:
+        name: Telegram-macOS-x86_64.app
+        path: ${{ github.workspace }}/out/Release/Telegram.app
+        if-no-files-found: error

.github/workflows/build-windows.yml

@@ -0,0 +1,101 @@
+name: Build Windows
+
+on:
+  push:
+    branches: [ master, main ]
+  pull_request:
+    branches: [ master, main ]
+
+jobs:
+  build:
+    runs-on: windows-2019 # Using windows-2019 for VS 2019, adjust if VS 2022 (windows-2022) is needed
+    env:
+      # Variables needed by prepare.py and build scripts
+      # Platform: x86, x64, arm64. This is usually set by the VS Native Tools Command Prompt.
+      # We'll use setup-msvc to achieve a similar environment.
+      # QT: As seen in prepare.py, this might be needed.
+      CHOCOLATEY_VERBOSITY: "fatal" # Make choco less noisy
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        submodules: 'recursive'
+
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.x' # prepare.py uses python
+
+    - name: Set up MSVC developer environment
+      uses: microsoft/setup-msvc-dev@v1
+      with:
+        arch: 'x64' # Or 'x86', 'arm64'. This sets up the %Platform% env var.
+        # vs-version: '16.0' # For VS 2019. For VS 2022 use '17.0' and windows-2022 runner.
+
+    - name: Install Inno Setup (if tsetup*.exe packaging is strictly part of compilation)
+      run: choco install innosetup --no-progress
+      # This is from build.bat, may not be needed if we only compile Telegram.exe and Updater.exe
+
+    - name: Install 7-Zip (if tportable*.zip packaging is strictly part of compilation)
+      run: choco install 7zip.install --no-progress
+      # This is from build.bat, may not be needed
+
+    - name: Cache Dependencies
+      id: cache-deps
+      uses: actions/cache@v3
+      with:
+        path: |
+          ${{ github.workspace }}/Libraries
+          ${{ github.workspace }}/ThirdParty
+        key: ${{ runner.os }}-${{ env.Platform }}-deps-${{ hashFiles('Telegram/build/prepare/prepare.py', 'Telegram/build/qt_version.py') }}
+        restore-keys: |
+          ${{ runner.os }}-${{ env.Platform }}-deps-
+
+    - name: Run prepare.py for dependencies
+      if: steps.cache-deps.outputs.cache-hit != 'true'
+      shell: cmd # prepare.py and its stages might use cmd-specific commands or rely on VS env
+      run: |
+        cd Telegram\build\prepare
+        python prepare.py skip-release
+        # prepare.py will build into Libraries and ThirdParty folders at the repo root.
+      env:
+        QT: '5.15.2' # Example, adjust as needed or determine from qt_version.py
+
+    - name: Configure build (emulating build.bat steps)
+      shell: cmd
+      run: |
+        cd Telegram
+        call configure.bat
+        # configure.bat should set up the 'out' directory.
+        # It uses %Platform% which is set by setup-msvc-dev.
+
+    - name: Build Telegram
+      shell: cmd
+      run: |
+        cd out
+        call cmake --build . --config Release --target Telegram -- /m:%NUMBER_OF_PROCESSORS%
+        # Using /m for parallel build with MSBuild (which CMake generates for VS)
+
+    - name: Upload Telegram.exe
+      uses: actions/upload-artifact@v4
+      with:
+        name: Telegram-windows-${{ env.Platform }}.exe
+        path: ${{ github.workspace }}/out/Release/Telegram.exe
+        if-no-files-found: error
+
+    - name: Upload Updater.exe
+      uses: actions/upload-artifact@v4
+      with:
+        name: Updater-windows-${{ env.Platform }}.exe
+        path: ${{ github.workspace }}/out/Release/Updater.exe
+        if-no-files-found: error
+
+    - name: Upload PDBs (optional)
+      uses: actions/upload-artifact@v4
+      with:
+        name: Symbols-windows-${{ env.Platform }}
+        path: |
+          ${{ github.workspace }}/out/Release/Telegram.pdb
+          ${{ github.workspace }}/out/Release/Updater.pdb
+        if-no-files-found: warn