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>

contracts/protocols.py

@@ -222,6 +222,7 @@ class FederationService(Protocol):
     async def get_outbox(
         self, session: AsyncSession, username: str,
         page: int = 1, per_page: int = 20,
+        origin_app: str | None = None,
     ) -> tuple[list[APActivityDTO], int]: ...
 
     async def get_activity_for_source(
@@ -236,6 +237,7 @@ class FederationService(Protocol):
     # -- Followers ------------------------------------------------------------
     async def get_followers(
         self, session: AsyncSession, username: str,
+        app_domain: str | None = None,
     ) -> list[APFollowerDTO]: ...
 
     async def get_followers_paginated(
@@ -247,10 +249,12 @@ class FederationService(Protocol):
         self, session: AsyncSession, username: str,
         follower_acct: str, follower_inbox: str, follower_actor_url: str,
         follower_public_key: str | None = None,
+        app_domain: str | None = None,
     ) -> APFollowerDTO: ...
 
     async def remove_follower(
         self, session: AsyncSession, username: str, follower_acct: str,
+        app_domain: str | None = None,
     ) -> bool: ...
 
     # -- Remote actors --------------------------------------------------------