feat: hide tunnel UI for terminal sessions and show session metadata

Backend:
- Add created_at to get_user_sessions response

Frontend:
- Hide tunnel error badges, probe output, and 'Recreate Tunnel' button for terminal-only sessions
- Show session start time (created_at) in active sessions list
- Show repository configuration (clone_mode, branch) for each session
- Skip health check polling for terminal-only sessions
- Update Session type to include created_at field

apps/web/src/api/sessions.ts

@@ -29,6 +29,7 @@ export interface Session {
   probe_status?: string;
   clone_mode?: string;
   branch?: string | null;
+  created_at?: string;
 }
 
 export async function listInstances(