Add origin_app to APActivity — apps only process their own activities

Each app's EventProcessor now filters by origin_app so apps don't steal
each other's pending activities. emit_activity() and publish_activity()
auto-detect the app name from Quart's current_app.

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

services/federation_impl.py

@@ -27,6 +27,14 @@ def _domain() -> str:
     return os.getenv("AP_DOMAIN", "rose-ash.com")
 
 
+def _get_origin_app() -> str | None:
+    try:
+        from quart import current_app
+        return current_app.name
+    except (ImportError, RuntimeError):
+        return None
+
+
 def _actor_to_dto(actor: ActorProfile) -> ActorProfileDTO:
     domain = _domain()
     username = actor.preferred_username
@@ -198,6 +206,7 @@ class SqlFederationService:
             source_id=source_id,
             visibility="public",
             process_state="pending",
+            origin_app=_get_origin_app(),
         )
         session.add(activity)
         await session.flush()