feat: Add browser mode fallback for Kaspersky audio blocking

- Add sidecar management to backend (sidecar_manager.py)
- Add sidecar API router for browser mode (/api/sidecar/*)
- Add browser-api.js polyfill for running in Chrome/Edge
- Add "Open in Browser" button when audio access fails
- Update build scripts with new sidecar modules
- Add start-browser.sh for development browser mode

Browser mode allows users to open the app in their system browser
when Electron's audio access is blocked by security software.
The backend manages the sidecar process in browser mode (BROWSER_MODE=true).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/build-client.bat

@@ -290,6 +290,8 @@ pyinstaller ^
     --hidden-import=app.routers.meetings ^
     --hidden-import=app.routers.ai ^
     --hidden-import=app.routers.export ^
+    --hidden-import=app.routers.sidecar ^
+    --hidden-import=app.sidecar_manager ^
     --collect-data=pydantic ^
     --collect-data=uvicorn ^
     run_server.py