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>

infrastructure/factory.py

@@ -144,7 +144,7 @@ def create_base_app(
             return await base_context()
 
     # --- event processor ---
-    _event_processor = EventProcessor()
+    _event_processor = EventProcessor(app_name=name)
 
     # --- startup ---
     @app.before_serving