Build Windows executable in shared Steam depot (#50)

## Summary
- install the nightly Windows MSVC target and cargo-xwin in CI
- build the production Windows executable alongside Linux
- package both executables and only imported_assets in one Steam depot

Reviewed-on: #50
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

.gitea/workflows/ci.yml

@@ -65,6 +65,11 @@ jobs:
           echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
           "$HOME/.cargo/bin/rustup" toolchain install nightly-2026-09-14 --profile minimal
 
+      - name: Install Windows build tooling
+        run: |
+          "$HOME/.cargo/bin/rustup" target add x86_64-pc-windows-msvc --toolchain nightly-2026-09-14
+          "$HOME/.cargo/bin/cargo" install cargo-xwin --locked
+
       - name: Cache production Rust dependencies and build artifacts
         uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
         with:
@@ -76,7 +81,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install --no-install-recommends -y \
-            clang \
+            clang-19 \
             libasound2-dev \
             libudev-dev \
             libusb-1.0-0-dev \
@@ -84,9 +89,15 @@ jobs:
             libx11-dev \
             libxkbcommon-dev \
             libxkbcommon-x11-0 \
+            lld-19 \
+            llvm-19 \
             mesa-vulkan-drivers \
             mold \
             pkg-config
+          sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-19 100
+          sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-19 100
+          echo "/usr/lib/llvm-19/bin" >> "$GITHUB_PATH"
+          rm -f "$HOME/.cache/cargo-xwin/clang-cl"
 
       - name: Preprocess assets
         run: cargo run --locked --bin process-assets --no-default-features --features debug_features -j 4
@@ -94,6 +105,11 @@ jobs:
       - name: Build production binary
         run: cargo build --locked --profile production --no-default-features --features debug_features -j 4
 
+      - name: Build Windows production binary
+        run: |
+          clang --version
+          cargo xwin build --locked --target x86_64-pc-windows-msvc --profile production --no-default-features --features debug_features -j 4 --bin shinespark
+
       - name: Verify production binary is not Bevy/Rust dynamically linked
         run: |
           ! readelf -d target/production/shinespark | grep -E 'libbevy_dylib|libstd-.*\.so'
@@ -101,10 +117,10 @@ jobs:
       - name: Package Linux Steam depot
         if: github.event_name == 'push' && github.ref == 'refs/heads/master'
         run: |
-          mkdir -p build/linux
-          cp target/production/shinespark build/linux/shinespark
-          cp -R assets build/linux/assets
-          cp -R imported_assets build/linux/imported_assets
+          mkdir -p build/game
+          cp target/production/shinespark build/game/shinespark
+          cp target/x86_64-pc-windows-msvc/production/shinespark.exe build/game/shinespark.exe
+          cp -R imported_assets build/game/imported_assets
 
       - if: github.event_name == 'push' && github.ref == 'refs/heads/master'
         uses: CyberAndrii/steam-totp@v1
@@ -123,5 +139,5 @@ jobs:
           appId: 3409670
           buildDescription: ${{ github.sha }}
           rootPath: build
-          depot1Path: linux
+          depot1Path: game
           releaseBranch: master