feat: add Windows cross-compilation and release artifacts

- Add mkWindowsCraneLib using x86_64-pc-windows-gnu target
- Add mkStreamdWindows using mingw-w64 toolchain for cross-compilation
- Export streamd-windows package from flake
- Add Windows build step and .exe artifact to release workflow

.forgejo/workflows/release.yml

@@ -49,12 +49,17 @@ jobs:
         if: steps.version.outputs.SKIP != 'true'
         run: nix build .#streamd-musl -o result-musl
 
+      - name: Build Windows binary
+        if: steps.version.outputs.SKIP != 'true'
+        run: nix build .#streamd-windows -o result-windows
+
       - name: Prepare release artifacts
         if: steps.version.outputs.SKIP != 'true'
         run: |
           mkdir -p release
           cp result-deb release/streamd_${{ steps.version.outputs.VERSION }}_amd64.deb
           cp result-musl/bin/streamd release/streamd-${{ steps.version.outputs.VERSION }}-linux-x86_64
+          cp result-windows/bin/streamd.exe release/streamd-${{ steps.version.outputs.VERSION }}-windows-x86_64.exe
 
       - name: Create release
         if: steps.version.outputs.SKIP != 'true'