Unify domain_events + ap_activities into AP-shaped event bus

All cross-service events now flow through ap_activities with a unified
EventProcessor. Internal events use visibility="internal"; federation
activities use visibility="public" and get delivered by a wildcard handler.

- Add processing columns to APActivity (process_state, actor_uri, etc.)
- New emit_activity() / register_activity_handler() API
- EventProcessor polls ap_activities instead of domain_events
- Rewrite all handlers to accept APActivity
- Migrate all 7 emit_event call sites to emit_activity
- publish_activity() sets process_state=pending directly (no emit_event bridge)
- Migration to drop domain_events table

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

events/handlers/login_handlers.py

@@ -2,24 +2,22 @@ from __future__ import annotations
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from shared.events import register_handler
-from shared.models.domain_event import DomainEvent
+from shared.events import register_activity_handler
+from shared.models.federation import APActivity
 from shared.services.registry import services
 
 
-async def on_user_logged_in(event: DomainEvent, session: AsyncSession) -> None:
-    payload = event.payload
-    user_id = payload["user_id"]
-    session_id = payload["session_id"]
+async def on_user_logged_in(activity: APActivity, session: AsyncSession) -> None:
+    data = activity.object_data
+    user_id = data["user_id"]
+    session_id = data["session_id"]
 
-    # Adopt cart items (if cart service is registered)
     if services.has("cart"):
         await services.cart.adopt_cart_for_user(session, user_id, session_id)
 
-    # Adopt calendar entries and tickets (if calendar service is registered)
     if services.has("calendar"):
         await services.calendar.adopt_entries_for_user(session, user_id, session_id)
         await services.calendar.adopt_tickets_for_user(session, user_id, session_id)
 
 
-register_handler("user.logged_in", on_user_logged_in)
+register_activity_handler("rose:Login", on_user_logged_in)