research: auto-transition processing → reviewing on last run

Hooks the topology_worker's post-terminal path into a new
notify_run_completed repo helper that atomically transitions the topic
processing → reviewing when the completed run has research_topic_id set
AND no siblings for that topic are still queued or running. Guarded on
status='processing' so a retry, a re-fire, or a topic already past
processing are all no-ops. Best-effort at the worker; DB hiccups are
logged and never fail the run.

The manual /submit-review endpoint stays as an escape hatch for topics
that end up parked in processing with nothing to complete (updated the
doc comment).

.sqlx/query-e26955627419e4773f72abb9010fcdcd589d777f0fd20b444a629feed2bf75e4.json

@@ -0,0 +1,22 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "UPDATE research_topics t\n            SET status = 'reviewing', updated_at = now()\n          WHERE t.id = (\n                    SELECT research_topic_id FROM topology_runs\n                     WHERE id = $1 AND research_topic_id IS NOT NULL\n                )\n            AND t.status = 'processing'\n            AND NOT EXISTS (\n                    SELECT 1 FROM topology_runs\n                     WHERE research_topic_id = t.id\n                       AND id <> $1\n                       AND status IN ('queued', 'running')\n                )\n          RETURNING t.id",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Uuid"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid"
+      ]
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "e26955627419e4773f72abb9010fcdcd589d777f0fd20b444a629feed2bf75e4"
+}