feat(render-parity): add deterministic frame comparison tool

- Introduced `render-parity` crate for comparing rendered frames against reference images.
- Added command-line options for specifying manifest and output directory.
- Implemented image comparison metrics: mean absolute difference, maximum absolute difference, and changed pixel ratio.
- Created a configuration file `cases.toml` for defining test cases with global defaults and specific parameters.
- Added functionality to capture frames from `render-demo` and save diff images on discrepancies.
- Updated documentation to include usage instructions and CI model for automated testing.

.gitea/workflows/test.yml

@@ -25,3 +25,31 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
       - name: Cargo test
         run: cargo test --workspace --all-features -- --nocapture
+
+  render-parity:
+    name: Render parity
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - uses: actions/checkout@v6
+      - uses: dtolnay/rust-toolchain@stable
+      - name: Install headless GL runtime
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y xvfb libgl1-mesa-dri libgles2-mesa-dev mesa-utils
+      - name: Build render-demo binary
+        run: cargo build -p render-demo --features demo
+      - name: Run frame parity suite
+        run: |
+          xvfb-run -s "-screen 0 1280x720x24" cargo run -p render-parity -- \
+            --manifest parity/cases.toml \
+            --output-dir target/render-parity/current \
+            --demo-bin target/debug/parkan-render-demo \
+            --keep-going
+      - name: Upload parity artifacts
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: render-parity-artifacts
+          path: target/render-parity/current
+          if-no-files-found: ignore