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>

.gitignore

@@ -50,5 +50,6 @@ Thumbs.db
 # Sidecar build artifacts
 src-tauri/binaries/*
 !src-tauri/binaries/.gitkeep
+src-tauri/sidecar.zip
 python/dist/
 python/build/