feat(app): version handshake — GUI restarts a stale running daemon

The daemon outlives the GUI, so after an update an OLD daemon can keep serving
the socket and the new GUI just connects to it (stale code — e.g. the missing
TERM fix). Both binaries are now stamped with the git build id (build.rs):
the daemon reports it in `health.build`, and on connect the bridge compares it
to the GUI's own SPACESH_BUILD; on mismatch it shuts the daemon down and lets
ensure_daemon respawn the bundled (matching) one. No-op for unstamped dev
builds or daemons too old to report a build. Build id is shown in Settings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/socketBridge.ts

@@ -178,7 +178,7 @@ export async function closeSurfaceCmd(surfaceId: string): Promise<void> {
   await invoke("close_surface", { surfaceId });
 }
 
-export interface DaemonHealth { version: string; pid: number; started_at_ms: number }
+export interface DaemonHealth { version: string; build?: string; pid: number; started_at_ms: number }
 
 export async function getHealth(): Promise<DaemonHealth> {
   return await invoke<DaemonHealth>("health");