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>

services/relationships.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 from sqlalchemy import select, func
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from shared.events import emit_event
+from shared.events import emit_activity
 from shared.models.container_relation import ContainerRelation
 
 
@@ -40,17 +40,19 @@ async def attach_child(
             if label is not None:
                 existing.label = label
             await session.flush()
-            await emit_event(
+            await emit_activity(
                 session,
-                event_type="container.child_attached",
-                aggregate_type="container_relation",
-                aggregate_id=existing.id,
-                payload={
+                activity_type="Add",
+                actor_uri="internal:system",
+                object_type="rose:ContainerRelation",
+                object_data={
                     "parent_type": parent_type,
                     "parent_id": parent_id,
                     "child_type": child_type,
                     "child_id": child_id,
                 },
+                source_type="container_relation",
+                source_id=existing.id,
             )
             return existing
         # Already attached and active — no-op
@@ -77,17 +79,19 @@ async def attach_child(
     session.add(rel)
     await session.flush()
 
-    await emit_event(
+    await emit_activity(
         session,
-        event_type="container.child_attached",
-        aggregate_type="container_relation",
-        aggregate_id=rel.id,
-        payload={
+        activity_type="Add",
+        actor_uri="internal:system",
+        object_type="rose:ContainerRelation",
+        object_data={
             "parent_type": parent_type,
             "parent_id": parent_id,
             "child_type": child_type,
             "child_id": child_id,
         },
+        source_type="container_relation",
+        source_id=rel.id,
     )
 
     return rel
@@ -139,17 +143,19 @@ async def detach_child(
     rel.deleted_at = func.now()
     await session.flush()
 
-    await emit_event(
+    await emit_activity(
         session,
-        event_type="container.child_detached",
-        aggregate_type="container_relation",
-        aggregate_id=rel.id,
-        payload={
+        activity_type="Remove",
+        actor_uri="internal:system",
+        object_type="rose:ContainerRelation",
+        object_data={
             "parent_type": parent_type,
             "parent_id": parent_id,
             "child_type": child_type,
             "child_id": child_id,
         },
+        source_type="container_relation",
+        source_id=rel.id,
     )
 
     return True