fix: resolve medium/low audit findings across backend and frontend

- ctx CLI: validate int() limit arg, wrap FTS5 MATCH in try/except
- ctx.rs: FTS5 error message clarity, Mutex::lock() returns Err not panic
- sdk-messages.ts: runtime type guards (str/num) replace bare `as` casts
- agent-runner.ts: strip ANTHROPIC_* env vars alongside CLAUDE*
- agent-dispatcher.ts: timestamps use seconds (match session.rs convention)
- remote.rs: disconnect handler uses lock().await not try_lock()
- session.rs: propagate pane_ids serialization error
- watcher.rs: reject root-level paths instead of silent no-op
- lib.rs: log warnings on profile.toml read failure and resource_dir error
- agent-bridge.ts: validate event payload is object before cast

v2/src/lib/adapters/agent-bridge.ts

@@ -56,7 +56,9 @@ export async function onSidecarMessage(
   callback: (msg: SidecarMessage) => void,
 ): Promise<UnlistenFn> {
   return listen<SidecarMessage>('sidecar-message', (event) => {
-    callback(event.payload as SidecarMessage);
+    const payload = event.payload;
+    if (typeof payload !== 'object' || payload === null) return;
+    callback(payload as SidecarMessage);
   });
 }