Fix sidecar.zip not bundled: move resources config into tauri.conf.json

The TAURI_CONFIG env var approach for resources wasn't being applied
by the NSIS bundler, so sidecar.zip was never included in the installer.

- Add resources: ["sidecar.zip"] directly to tauri.conf.json
- build.rs creates a minimal placeholder zip for dev builds so
  compilation succeeds even without the real sidecar
- Remove TAURI_CONFIG env var from all CI workflows (no longer needed)
- Add sidecar.zip to .gitignore (generated by CI, not tracked)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/build-macos.yml

@@ -62,8 +62,6 @@ jobs:
 
       - name: Build Tauri app
         run: npm run tauri build
-        env:
-          TAURI_CONFIG: '{"bundle":{"resources":["sidecar.zip"]}}'
 
       # ── Release ──
       - name: Upload to release