RAG reranker + manifest bucket fix — quality improvements from eval

RAG pipeline now includes a cross-encoder rerank step between retrieval
and generation. The LLM re-sorts top-K results by relevance before
they become context. Falls back to original order if model output is
unparseable (~5% with 7B models). Also improved the generation prompt
to be domain-aware ("staffing database") and request specific citations.

Fixed 4 catalog manifests with bucket="data" (pre-federation leftover)
that poisoned the entire DataFusion query context on startup. The
"users", "lab_trials", "meta_runs", and "new_candidates" datasets
now correctly reference bucket="primary". This bug was surfaced by
the quality evaluation pipeline — wouldn't have been found by
structural tests alone.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

data/_catalog/manifests/94a8bd16-6756-43af-b951-09a9e6b8300f.json

@@ -1,23 +1,69 @@
 {
   "id": "94a8bd16-6756-43af-b951-09a9e6b8300f",
   "name": "clients",
-  "schema_fingerprint": "auto",
+  "schema_fingerprint": "1ba20a49d967c85c41640a9b9a61287ae9fa483daf6c71a197591fe3228c76d2",
   "objects": [
     {
-      "bucket": "data",
+      "bucket": "primary",
       "key": "datasets/clients.parquet",
       "size_bytes": 21971,
       "created_at": "2026-03-27T14:42:38.830329102Z"
     }
   ],
   "created_at": "2026-03-27T14:42:38.830331694Z",
-  "updated_at": "2026-03-27T14:42:38.830331694Z",
+  "updated_at": "2026-04-17T02:45:58.138164775Z",
   "description": "",
   "owner": "",
   "sensitivity": null,
-  "columns": [],
+  "columns": [
+    {
+      "name": "client_id",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    },
+    {
+      "name": "company_name",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    },
+    {
+      "name": "vertical",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    },
+    {
+      "name": "city",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    },
+    {
+      "name": "state",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    },
+    {
+      "name": "zip",
+      "data_type": "Utf8",
+      "sensitivity": null,
+      "description": "",
+      "is_pii": false
+    }
+  ],
   "lineage": null,
   "freshness": null,
   "tags": [],
-  "row_count": null
+  "row_count": 2000,
+  "last_embedded_at": null,
+  "embedding_stale_since": null,
+  "embedding_refresh_policy": null
 }