feat(mobile): per-user device bindings, multi-user Inbox routing, and admin-mediated authorization

- Device→user bindings persisted in config table (auth.rs), loaded at plugin start
- RelayApp now routes Inbox responses per-user via UserChannelApi, never globally
- New mobile_bind_device LLM tool for admin-mediated device→user assignment
- Per-user event forwarders (events.rs) with per-user debounced notifiers
- Config listener (auth::config_listener) refreshes bindings cache reactively
- Reconcile loop catches users who unlock after boot
- Hello/Logout treated as device-registry ops (no user resolution needed)
- Unbound device payloads are silently dropped
- RelayAgent::authorize_client → bind_device (atomic bind + authorize)
- Approval rules seed mobile_bind_device/revoke_device as require

crates/plugin-mobile-connector/src/payloads.rs

@@ -103,7 +103,10 @@ pub fn build_inbox_update(snapshot: &InboxSnapshot) -> Value {
     })
 }
 
-/// Build a generic `notification` payload (payloads.md §3.2).
+/// Build a generic `notification` payload (payloads.md §3.2). Part of the wire
+/// contract; retained for the protocol surface even though the current per-user
+/// flow pushes Inbox updates rather than free-form notifications.
+#[allow(dead_code)]
 pub fn build_notification(title: &str, body: &str) -> Value {
     serde_json::json!({
         "v": 1,