Previously, running `bun run dev` would fail because Tauri requires
the sidecar binary to exist at compile time, even in development mode.
This forced developers to build the full PyInstaller binary before
they could start development.
This change introduces a streamlined dev workflow:
1. Add `scripts/setup-dev-sidecar.js` - Creates minimal placeholder
binaries that satisfy Tauri's compile-time check. Works cross-platform
(Windows PE stub, Unix shell script).
2. Update Rust code to gracefully handle dev mode - When the sidecar
fails to start, it checks if a manually-started server is already
running on the expected port and connects to it instead.
3. Update npm scripts - `bun run dev` now auto-runs the setup script,
and `dev:server` uses the correct port (17493).
4. Update CONTRIBUTING.md with clearer dev workflow documentation.
New development workflow:
Terminal 1: bun run dev:server
Terminal 2: bun run dev
The bundled binary is only required for production builds.
