Add fediverse social tables, protocols, and implementations

6 new ORM models (remote actors, following, remote posts, local posts,
interactions, notifications), 20 new FederationService methods with
SQL implementations and stubs, WebFinger client, and Alembic migration.

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

services/stubs.py

@@ -227,5 +227,65 @@ class StubFederationService:
     async def remove_follower(self, session, username, follower_acct):
         return False
 
+    async def get_or_fetch_remote_actor(self, session, actor_url):
+        return None
+
+    async def search_remote_actor(self, session, acct):
+        return None
+
+    async def send_follow(self, session, local_username, remote_actor_url):
+        raise RuntimeError("FederationService not available")
+
+    async def get_following(self, session, username, page=1, per_page=20):
+        return [], 0
+
+    async def accept_follow_response(self, session, local_username, remote_actor_url):
+        pass
+
+    async def unfollow(self, session, local_username, remote_actor_url):
+        pass
+
+    async def ingest_remote_post(self, session, remote_actor_id, activity_json, object_json):
+        pass
+
+    async def delete_remote_post(self, session, object_id):
+        pass
+
+    async def get_remote_post(self, session, object_id):
+        return None
+
+    async def get_home_timeline(self, session, actor_profile_id, before=None, limit=20):
+        return []
+
+    async def get_public_timeline(self, session, before=None, limit=20):
+        return []
+
+    async def create_local_post(self, session, actor_profile_id, content, visibility="public", in_reply_to=None):
+        raise RuntimeError("FederationService not available")
+
+    async def delete_local_post(self, session, actor_profile_id, post_id):
+        raise RuntimeError("FederationService not available")
+
+    async def like_post(self, session, actor_profile_id, object_id, author_inbox):
+        pass
+
+    async def unlike_post(self, session, actor_profile_id, object_id, author_inbox):
+        pass
+
+    async def boost_post(self, session, actor_profile_id, object_id, author_inbox):
+        pass
+
+    async def unboost_post(self, session, actor_profile_id, object_id, author_inbox):
+        pass
+
+    async def get_notifications(self, session, actor_profile_id, before=None, limit=20):
+        return []
+
+    async def unread_notification_count(self, session, actor_profile_id):
+        return 0
+
+    async def mark_notifications_read(self, session, actor_profile_id):
+        pass
+
     async def get_stats(self, session):
         return {"actors": 0, "activities": 0, "followers": 0}