Add per-app AP social UI for blog, market, and events

Lightweight social pages (search, follow/unfollow, followers, following,
actor timeline) auto-registered for AP-enabled apps via shared blueprint.
Federation keeps the full social hub. Followers scoped per app_domain;
post cards show "View on Hub" link instead of interaction buttons.

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

shared/services/federation_impl.py

@@ -403,6 +403,7 @@ class SqlFederationService:
     async def get_followers_paginated(
         self, session: AsyncSession, username: str,
         page: int = 1, per_page: int = 20,
+        app_domain: str | None = None,
     ) -> tuple[list[RemoteActorDTO], int]:
         actor = (
             await session.execute(
@@ -412,11 +413,13 @@ class SqlFederationService:
         if actor is None:
             return [], 0
 
+        filters = [APFollower.actor_profile_id == actor.id]
+        if app_domain is not None:
+            filters.append(APFollower.app_domain == app_domain)
+
         total = (
             await session.execute(
-                select(func.count(APFollower.id)).where(
-                    APFollower.actor_profile_id == actor.id,
-                )
+                select(func.count(APFollower.id)).where(*filters)
             )
         ).scalar() or 0
 
@@ -424,7 +427,7 @@ class SqlFederationService:
         followers = (
             await session.execute(
                 select(APFollower)
-                .where(APFollower.actor_profile_id == actor.id)
+                .where(*filters)
                 .order_by(APFollower.created_at.desc())
                 .limit(per_page)
                 .offset(offset)

shared/services/stubs.py

@@ -28,5 +28,15 @@ class StubFederationService:
     async def count_activities_for_source(self, session, source_type, source_id, *, activity_type):
         return 0
 
+    async def get_followers_paginated(self, session, username,
+                                      page=1, per_page=20, app_domain=None):
+        return [], 0
+
+    async def get_following(self, session, username, page=1, per_page=20):
+        return [], 0
+
+    async def search_actors(self, session, query, page=1, limit=20):
+        return [], 0
+
     async def get_stats(self, session):
         return {"actors": 0, "activities": 0, "followers": 0}