audit: resident website loop architecture and code quality to 10/10

Fix F1 name race with partial unique index, F2 pause/end mid-poll race with guarded updates, F3 redirect/numeric-IP SSRF, F4 quota prefix check, F5 duplicate row_get, F6 audit ternary; S1 unused import, S2 backoff doc, S3 defensive tearDown. Directed 20 pass, full 1700 pass.

cloud/server.py

@@ -10245,13 +10245,11 @@ class CloudControlPlaneHandler(BaseHTTPRequestHandler):
                     "error": "resident watch in status %s cannot %s"
                              % (watch["status"], action)})
             return
+        audit_action = {"pause": "resident_watch_paused",
+                        "resume": "resident_watch_resumed",
+                        "end": "resident_watch_ended"}[action]
         with _auth_store(self.server.db_path) as store:
-            store.audit(user_id, project_id,
-                        "resident_watch_%s" % ("ended" if action == "end"
-                                               else action + "d"
-                                               if action == "pause"
-                                               else "resumed"),
-                        watch_id)
+            store.audit(user_id, project_id, audit_action, watch_id)
         self._send_json(200, watch)
 
     def _triage_inbox(self, project_id):