feat: Add Electron support via Rust sidecar

[google-labs-jules]

This PR adds support for compiling and running the Jan application using Electron, while reusing the existing Rust backend as a sidecar process.

Key changes:

1. Rust Backend (src-tauri):

   • Added server_mode.rs: An HTTP server that maps API endpoints to internal Rust commands (e.g., /api/list_threads -> core::threads::commands::list_threads).
   • Modified lib.rs: Detects --electron CLI argument. If present, it hides the main window and starts the HTTP server on a random port, printing the port to stdout.

2. Frontend (web-app):

   • Added isPlatformElectron detection.
   • Updated service.ts to use a new transport layer when running in Electron:
     • UI commands (dialogs) are sent to Electron Main process via IPC.
     • Logic commands (AI, threads, settings) are sent to the Rust sidecar via HTTP fetch.
   • Updated PlatformFeatures to enable desktop features for Electron.

3. Electron App (electron-app):

   • Created a new package @jan/electron-app.
   • main.ts: Spawns the Rust binary with --electron flag, captures the port, and creates a BrowserWindow.
   • Registers asset:// protocol to serve local files (replacing Tauri's convertFileSrc behavior).
   • Configured electron-builder to bundle the compiled Rust binary and the React frontend assets.

4. Build System:

   • Added electron-app to Yarn workspaces.
   • Added dev:electron and build:electron scripts to root package.json.

Verification:

• Verified yarn build:electron successfully packages the application.
• Verified cargo test passes in src-tauri.
• Verified web-app builds successfully for web target.

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PR created automatically by Jules for task 6661250475688752829 started by @Juude

[google-labs-jules]

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