# Change: Add Embedded Backend Packaging for All-in-One Deployment

## Why
Currently, deploying Meeting Assistant requires setting up both the Electron client and a separate backend server. For enterprise internal deployment, users want a simpler experience: **double-click the exe and it works** without needing to understand or configure backend services separately.

Additionally, when users first run the packaged application, the Whisper model download (~1.5GB) shows only "loading_model" status with no progress indication, causing confusion about whether the download is actually happening.

## What Changes
- **New capability: Embedded Backend** - Package FastAPI backend as a sidecar managed by Electron
- **Backend sidecar management** - Electron starts/stops backend process automatically
- **Health check mechanism** - Wait for backend readiness before loading frontend
- **Configuration unification** - All settings (DB, API keys, auth) in single `config.json`
- **Backward compatible** - Existing deployment method (separate backend) still works via `backend.embedded: false` flag
- **Model download progress** - Show real-time download percentage for Whisper model

## Impact
- Affected specs: `embedded-backend` (new), `transcription` (modified)
- Affected code:
  - `backend/run_server.py` (new) - Backend entry point for packaging
  - `backend/build.py` (new) - PyInstaller build script
  - `backend/app/config.py` - Support frozen executable paths
  - `client/src/main.js` - Backend sidecar management
  - `client/src/preload.js` - Expose backend status API
  - `client/config.json` - Extended configuration schema
  - `client/package.json` - Build configuration for backend resources
  - `sidecar/transcriber.py` - Model download progress reporting
  - `scripts/build-client.bat` - Integrated build script
  - `scripts/build-all.ps1` - PowerShell build script