feat: 迁移统一目录元数据契约 (#102)

## 中文

- 为 System Agent、34 个 Builtin Skill、28 个 Pointer/Collection 条目增加 catalog
sidecar
- 覆盖 147 个 collection child，并固定可证明的来源；无法证明的内容保持 listing-only/unknown
- 增加 strict Schema、validator、collection check 与 CI 完整性门禁

## English

- Add catalog metadata sidecars for the System Agent, 34 built-in
Skills, and 28 pointer/collection entries
- Cover 147 collection children while keeping unverifiable facts
listing-only or unknown
- Add strict schemas, validators, deterministic collection checks, and
CI completeness gates

## 验证 / Verification

- Catalog validator 17/17
- Collection generator 4/4
- 63 sidecars, 147 children, zero errors

skills/taste-skill/entry.json

@@ -31,6 +31,7 @@
     "kind": "git",
     "repoUrl": "https://github.com/Leonxlnx/taste-skill.git",
     "repoBranch": "main",
-    "path": "skills/taste-skill"
+    "path": "skills/taste-skill",
+    "ref": "ccbc15639c97057cbfcf32ecebc38ef716e4bb37"
   }
 }