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>

src-tauri/tauri.conf.json

@@ -42,6 +42,7 @@
     "category": "Utility",
     "shortDescription": "Transcribe audio/video with speaker identification",
     "longDescription": "Voice to Notes is a desktop application that transcribes audio and video recordings with speaker identification, synchronized playback, and AI-powered analysis. Export to SRT, WebVTT, ASS captions, or plain text.",
+    "resources": ["sidecar.zip"],
     "copyright": "Voice to Notes Contributors",
     "license": "MIT",
     "linux": {