feat: add search_scope to all teachers + cross-reference tool for inter-teacher dialogue

Each teacher's meta.json now includes search_scope with tradition-specific
CBETA/SuttaCentral IDs, dictionary sources, and keywords for focused RAG
retrieval. New tools/cross_reference.py enables lineage queries and
cross-tradition concept comparison via FoJin KG.

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

prebuilt/xuyun/meta.json

@@ -4,16 +4,57 @@
   "tradition": "汉传",
   "school": "禅宗（五宗兼嗣）",
   "era": "1840-1959",
-  "languages": ["zh"],
+  "languages": [
+    "zh"
+  ],
   "fojin_entity_id": null,
   "sources": [
-    {"type": "cbeta", "id": "T19n0945", "title": "大佛顶首楞严经"},
-    {"type": "cbeta", "id": "T08n0235", "title": "金刚般若波罗蜜经"},
-    {"type": "cbeta", "id": "T48n2008", "title": "六祖大师法宝坛经"},
-    {"type": "cbeta", "id": "T17n0842", "title": "大方广圆觉修多罗了义经"}
+    {
+      "type": "cbeta",
+      "id": "T19n0945",
+      "title": "大佛顶首楞严经"
+    },
+    {
+      "type": "cbeta",
+      "id": "T08n0235",
+      "title": "金刚般若波罗蜜经"
+    },
+    {
+      "type": "cbeta",
+      "id": "T48n2008",
+      "title": "六祖大师法宝坛经"
+    },
+    {
+      "type": "cbeta",
+      "id": "T17n0842",
+      "title": "大方广圆觉修多罗了义经"
+    }
   ],
   "version": "1.0.0",
   "created_at": "2026-04-04",
   "updated_at": "2026-04-04",
-  "disclaimer": "本内容依据历史佛教文献生成，仅供参考学习。如需正式修行指导，请亲近善知识。"
+  "disclaimer": "本内容依据历史佛教文献生成，仅供参考学习。如需正式修行指导，请亲近善知识。",
+  "search_scope": {
+    "primary_cbeta_ids": [
+      "T19n0945",
+      "T08n0235",
+      "T48n2008",
+      "T17n0842"
+    ],
+    "traditions": [
+      "禅宗"
+    ],
+    "dictionary_sources": [
+      "foguang",
+      "dingfubao"
+    ],
+    "keywords": [
+      "参禅",
+      "话头",
+      "疑情",
+      "开悟",
+      "禅七",
+      "禅净双修"
+    ]
+  }
 }