修復中文路徑 preflight 與 BM25 核心詞落空，測資改照現實建

兩個 bug 同源於自檢測資「照能過建、不照現實建」：

- ingest preflight：git status --porcelain 預設會把含中文或空格的路徑加引號
  轉義，raw/ 白名單比對因此失效，中文檔名的 convert 產出被誤判為 raw/ 以外的
  未提交變更而中止攝入。舊測資用 ASCII 檔名，整條路徑從未被走過。

- search：BM25Okapi 的 idf 在 df >= N/2 時 <= 0（rank_bm25 對負 idf 的替代值
  epsilon x average_idf 在 average_idf 為負時同樣為負），與 search() 的 s > 0
  過濾相乘，會讓「每頁都提到的核心詞」查詢全數落空——知識庫愈小、詞愈核心
  愈嚴重，MCP 的 search_wiki 一併受害。改用 Lucene 式恆正 idf。
  舊測資每個查詢詞都只出現在一頁（df=1），恰好避開此配置。

變更：
- tools/ingest.py：preflight 比對前剝除 git 的轉義引號
- tools/search.py：_BM25 子類覆寫 _calc_idf 為 log(1 + (N-df+0.5)/(df+0.5))
- tools/selfcheck_ingest.py：新增 preflight 中文檔名放行 / 非 raw 擋下的檢查
- tools/selfcheck_search.py：新增與既有頁共用核心詞的測資，鎖住 idf 退化
- tools/convert/selfcheck.py、tools/selfcheck_lint.py：測資檔名改中文＋空格
- AGENTS.md §13.4：新增「測資照現實建，不是照能過建」規則
- README.md §3.2：補 convert 產出應保持未提交、由 ingest 一併 commit 的流程

驗證：四個自檢全數通過；分別移除兩個修法後對應檢查會失敗。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/selfcheck_lint.py

@@ -23,6 +23,8 @@ limits: {mcp_response_max_tokens: 2000, ingest_chunk_max_chars: 12000}
 """
 SHA_A = "abcd1234" + "0" * 56
 SHA_B = "beef5678" + "0" * 56
+SRC_OK = "raw/converted/好來源 報告.md"
+SRC_UNCOVERED = "raw/converted/未覆蓋 來源.md"
 
 
 def page(root, rel, meta, body="內文。"):
@@ -36,20 +38,22 @@ def build(root):
     for sub in ("config", "raw/converted", "wiki/summaries", "wiki/entities", "wiki/concepts"):
         (root / sub).mkdir(parents=True)
     (root / "config/models.yaml").write_text(CFG, encoding="utf-8")
+    # 來源檔名一律「中文 + 空格」——真實 QA 文件就長這樣（§12：測資要照現實建，不是照能過建）
     (root / "raw/manifest.json").write_text(json.dumps({"version": 1, "files": {
-        "raw/converted/good-src.md": {"kind": "converted", "sha256": SHA_A,
-                                      "original_path": "raw/originals/g.docx",
-                                      "original_sha256": SHA_A, "converter": "from_docx",
-                                      "converted_at": "2026-07-01T00:00:00"},
-        "raw/converted/uncovered.md": {"kind": "converted", "sha256": SHA_B,
-                                       "original_path": "raw/originals/u.docx",
-                                       "original_sha256": SHA_B, "converter": "from_docx",
-                                       "converted_at": "2026-07-01T00:00:00"},
-        "raw/originals/scan.pdf": {"kind": "original", "sha256": SHA_B,
-                                   "media_type": "pdf", "added_at": "2026-07-01T00:00:00",
-                                   "status": "needs_ocr"},
+        SRC_OK: {"kind": "converted", "sha256": SHA_A,
+                 "original_path": "raw/originals/好來源 報告.docx",
+                 "original_sha256": SHA_A, "converter": "from_docx",
+                 "converted_at": "2026-07-01T00:00:00"},
+        SRC_UNCOVERED: {"kind": "converted", "sha256": SHA_B,
+                        "original_path": "raw/originals/未覆蓋 來源.docx",
+                        "original_sha256": SHA_B, "converter": "from_docx",
+                        "converted_at": "2026-07-01T00:00:00"},
+        "raw/originals/掃描件 無文字層.pdf": {"kind": "original", "sha256": SHA_B,
+                                             "media_type": "pdf",
+                                             "added_at": "2026-07-01T00:00:00",
+                                             "status": "needs_ocr"},
     }}), encoding="utf-8")
-    ref = f"raw/converted/good-src.md#{SHA_A[:8]}"
+    ref = f"{SRC_OK}#{SHA_A[:8]}"
     good = {"type": "entity", "title": "支付閘道", "description": "支付閘道模組",
             "tags": ["gateway"], "timestamp": today, "sources": [ref], "status": "draft"}
     page(root, "wiki/entities/good.md", good)
@@ -90,7 +94,7 @@ def main():
         assert code == 1, code
         report = next((root / "reports").glob("lint-*.md")).read_text(encoding="utf-8")
         for expected in ("缺欄位 tags", "source_ref 不在 manifest",
-                         "old.md", "建議人工複審", "uncovered.md", "攝入缺口",
+                         "old.md", "建議人工複審", "未覆蓋 來源.md", "攝入缺口",
                          "needs_ocr", "bad-schema.md` — 不被 index.md"):
             assert expected in report, f"報告缺少：{expected}\n{report}"
         assert "good.md" not in report