feat(04-02): pinned golden corpus + D-14 corpus runner + Nyquist gate

- golden-corpus.json: 75 hand-written pinned cases (D-13) — landmark 17 /
  abbreviation 15 / glued 7 / typo 14 / alias 15 / negative 7, incl. two
  near-miss negatives (Penang 0.625, Kampung Cina ~0.58) below the 0.72
  admission line; threshold.top3_hit_rate pinned at 0.9
- gazetteer-corpus.mjs: the D-14 runner — imports the SAME src/index.ts the
  bot uses, measures top-1/top-3 + per-category rates + avg ms/query, prints
  the refusal margin and the fixed escalation ladder on failure, exports
  measureCorpus() for the in-process suite, exits 0 only on threshold + zero leaks
- corpus.test.mjs goes green: CO1-CO8 (the Nyquist gate inside npm run search:test)
- delegates: search:corpus (root) + corpus (search workspace)

Measured: top-3 68/68 (100.0%) >= 90%, negatives refused 7/7, margin 0.643 < 0.72 —
threshold met on the first run (D-14 lever: None).

package.json

@@ -25,6 +25,7 @@
     "web:typecheck": "npm run typecheck -w web",
     "search:test": "npm test -w search",
     "search:typecheck": "npm run typecheck -w search",
+    "search:corpus": "node search/scripts/gazetteer-corpus.mjs",
     "web:dev": "npm run dev -w web",
     "web:build": "npm run build -w theme && npm run build -w web",
     "web:build:harness": "npm run build:harness -w web",