Add production build pipeline (#46)

## Summary
- split development dynamic linking from production builds
- add headless processed-asset generation
- add a separate production CI cache and static Bevy/Rust linkage verification
- keep custom debug features enabled for production builds behind a feature gate

Reviewed-on: #46
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

.gitea/workflows/ci.yml

@@ -50,3 +50,50 @@ jobs:
 
       - name: Run unit tests
         run: cargo test --locked --lib -j 4
+
+  production-build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+    steps:
+      - name: Check out source
+        uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
+            sh -s -- -y --profile minimal
+          echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
+          "$HOME/.cargo/bin/rustup" toolchain install nightly-2026-09-14 --profile minimal
+
+      - name: Cache production Rust dependencies and build artifacts
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          prefix-key: v2-rust
+          shared-key: linux-nightly-production
+          cache-bin: false
+
+      - name: Install Linux dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install --no-install-recommends -y \
+            clang \
+            libasound2-dev \
+            libudev-dev \
+            libusb-1.0-0-dev \
+            libwayland-dev \
+            libx11-dev \
+            libxkbcommon-dev \
+            libxkbcommon-x11-0 \
+            mesa-vulkan-drivers \
+            mold \
+            pkg-config
+
+      - name: Preprocess assets
+        run: cargo run --locked --bin process-assets --no-default-features --features debug_features -j 4
+
+      - name: Build production binary
+        run: cargo build --locked --profile production --no-default-features --features debug_features -j 4
+
+      - name: Verify production binary is not Bevy/Rust dynamically linked
+        run: |
+          ! readelf -d target/production/shinespark | grep -E 'libbevy_dylib|libstd-.*\.so'