feat(routines): deliver notifications to all installed channels (#398)

* feat(routines): deliver notifications to all installed channels

Routine notifications were silently lost because the forwarder didn't
use NotifyConfig fields and WASM channels (Telegram, Slack) had
broadcast() as a no-op. This fixes three issues:

1. send_notification() now includes notify_user/notify_channel in
   metadata so the forwarder can route to specific channels
2. The routine forwarder mirrors the heartbeat pattern: try targeted
   channel first, fall back to broadcast_all
3. WasmChannel implements broadcast() using last-seen message metadata
   (chat_id), with persistence to the settings table so it survives
   restarts. Only writes to DB when the value actually changes.

Heartbeat notifications also benefit from the WASM broadcast fix.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* refactor(wasm): extract do_update_broadcast_metadata to eliminate duplication

The inline metadata-update block in `dispatch_emitted_messages` was
identical to the `update_broadcast_metadata` instance method. Extract
the shared logic into a private free function `do_update_broadcast_metadata`
that both call, so the persistence logic lives in one place.

Addresses Gemini code review comment on PR #398.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

---------

Co-authored-by: Claude Sonnet 4.6 <[email protected]>

src/agent/routine_engine.rs

@@ -605,6 +605,8 @@ async fn send_notification(
             "source": "routine",
             "routine_name": routine_name,
             "status": status.to_string(),
+            "notify_user": notify.user,
+            "notify_channel": notify.channel,
         }),
     };