feat: wire Timeline activity endpoint + surface source_channel

/api/activity and /api/activity-feed were never registered in app.py —
both files existed but neither route was reachable (confirmed 404 on VPS).
Register both so Timeline and gamification feeds can consume them.

Adds source_channel to /api/activity payload (both PR rows and audit
events — audit rows return null since they aren't tied to a specific PR).
Migration v22 already populated prs.source_channel on VPS with enum:
telegram=2340, agent=698, maintenance=102, unknown=11, github=1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

diagnostics/activity_endpoint.py

@@ -143,7 +143,7 @@ async def handle_activity(request):
         # Each PR generates events at created_at and merged_at timestamps
         pr_query = """
             SELECT number, status, domain, agent, branch, source_path,
-                   created_at, merged_at
+                   created_at, merged_at, source_channel
             FROM prs
             WHERE {where_clause}
             ORDER BY COALESCE(merged_at, created_at) DESC
@@ -189,6 +189,7 @@ async def handle_activity(request):
                 'description': description,
                 'status': row_dict['status'],
                 'pr_number': row_dict['number'],
+                'source_channel': row_dict.get('source_channel') or 'unknown',
             })
 
         # Source 2: Audit log events (secondary — pipeline-level)
@@ -228,6 +229,7 @@ async def handle_activity(request):
                     'description': description,
                     'status': None,
                     'pr_number': None,
+                    'source_channel': None,  # audit events not tied to a PR
                 })
 
         conn.close()

diagnostics/app.py

@@ -2283,6 +2283,12 @@ def create_app() -> web.Application:
     # Response audit - cost tracking + reasoning traces
     app["db_path"] = str(DB_PATH)
     register_response_audit_routes(app)
+    # Timeline activity feed (per-PR + audit_log events for dashboard v2)
+    from activity_endpoint import handle_activity
+    app.router.add_get("/api/activity", handle_activity)
+    # Gamification activity feed (hot/recent/important sort)
+    from activity_feed_api import register as register_activity_feed
+    register_activity_feed(app)
     app.on_cleanup.append(_cleanup)
     return app