- unified_search and GitHubSource.search dedup: replace naive
`trust_level == "trusted"` check with ranked comparison so
"builtin" results are never overwritten by "trusted" or "community"
- Add 43 unit tests covering _parse_frontmatter_quick, trust_level_for,
HubLockFile CRUD, TapsManager ops, LobeHub _convert_to_skill_md,
unified_search dedup (with regression test), and append_audit_log