Add per-app ActivityPub actors via shared AP blueprint

Each AP-enabled app (blog, market, events, federation) now serves its
own webfinger, actor profile, inbox, outbox, and followers endpoints.
Per-app actors are virtual projections of the same ActorProfile/keypair,
scoped by APFollower.app_domain and APActivity.origin_app.

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

events/handlers/ap_delivery_handler.py

@@ -131,10 +131,30 @@ async def on_any_activity(activity: APActivity, session: AsyncSession) -> None:
         log.warning("Actor not found or missing key for activity %s", activity.activity_id)
         return
 
-    # Load followers
+    # Load followers: aggregate (app_domain IS NULL) always get everything.
+    # If the activity has an origin_app, also include app-specific followers.
+    from sqlalchemy import or_
+
+    follower_filters = [
+        APFollower.actor_profile_id == actor.id,
+    ]
+
+    origin_app = activity.origin_app
+    if origin_app and origin_app != "federation":
+        # Aggregate followers (NULL) + followers of this specific app
+        follower_filters.append(
+            or_(
+                APFollower.app_domain.is_(None),
+                APFollower.app_domain == origin_app,
+            )
+        )
+    else:
+        # Federation / no origin_app: deliver to all followers
+        pass
+
     followers = (
         await session.execute(
-            select(APFollower).where(APFollower.actor_profile_id == actor.id)
+            select(APFollower).where(*follower_filters)
         )
     ).scalars().all()
 
@@ -142,7 +162,7 @@ async def on_any_activity(activity: APActivity, session: AsyncSession) -> None:
         log.debug("No followers to deliver to for %s", activity.activity_id)
         return
 
-    # Deduplicate inboxes
+    # Deduplicate inboxes (same remote actor may follow both aggregate + app)
     all_inboxes = {f.follower_inbox for f in followers if f.follower_inbox}
 
     # Check delivery log — skip inboxes we already delivered to (idempotency)