fix(skills): make all skills load-valid + add scripts/verify_skills.py

Add a comprehensive load verifier and fix the two issues it found:

- scripts/verify_skills.py: validates every loadable unit (flat root, suite sub-skill,
  plugin skill) with real YAML parsing, name regex + global uniqueness, frontmatter
  <=1024, description sanity, plugin.json JSON validity, and orphan detection. Read-only.
- 92-tui-design-template (root + code/SKILL.md): fix invalid YAML `triggers:` block
  (`- "a", "b"` multi-scalar list items) -> one phrase per list item.
- 17-seo-schema-generator: remove ">" from description ("generate -> validate" ->
  "generate then validate"); angle brackets are disallowed in descriptions.

Result: 75/75 loadable skills valid — 0 failures, 0 name collisions, 0 orphans,
0 plugin-manifest errors (65 flat + 3 plugins + 7 suite sub-skills).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/17-seo-schema-generator/SKILL.md

@@ -6,7 +6,7 @@ description: |
   (2) from collected sources for a not-yet-published site — reconcile conflicting
   facts into a provenance-tracked claims register. Both modes emit the same claims
   register, build pruned drafts from type templates (no placeholders shipped), and
-  hand off to 16-seo-schema-validator (generate -> validate, gate = zero P0).
+  hand off to 16-seo-schema-validator (generate then validate, gate = zero P0).
   Triggers: generate schema, create JSON-LD, schema markup, structured data generator,
   source-to-schema, pre-launch schema, claims register, 스키마 생성, 스키마 저작,
   구조화 데이터 생성, 미발행 사이트 스키마, 기존 사이트 스키마 추출.