refactor(skill): rename validate → web-validate

Clearer scoped name for the W3C + WCAG skill. Updated: folder (git mv),
frontmatter name, H1 title, command refs, CLAUDE.md routing, 6 profiles
(functional — activate the skill by folder name), cross-refs in
harden/seo/depth-matrix/client-handover, agent dispatch refs, README +
USAGE tables.

Confidentiality: the client-deliverable leak-guard regex
(client-handover-writer.md) now matches BOTH /web-validate and legacy
/validate, so older client docs stay covered.

Left intentionally: validator-analyzer agent name (lockstep with
subagent_type + registry), .validate-cache/ + VALIDATE.md (audit-file
family {SEO,GEO,HARDEN,CSO,VALIDATE}.md), .claude/ history (append-only),
CHANGELOG old entry (added a new "renamed" entry instead). NL trigger
keywords kept so "validate" still routes here. Third-party html-validate
untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W9sqAwZxBMZSynZoVrEJhd

skills/seo/resources/depth-matrix.md

@@ -30,8 +30,8 @@ LOCAL caps at 20. FULL caps at 20. Never report above 20.
 
 | Finding type | Owner skill | If reported by /seo, what to do |
 |---|---|---|
-| HTML validity errors (W3C nu validator) | /validate | Drop from /seo report; note `"see /validate report for HTML validity"`. |
-| WCAG accessibility | /validate | Drop. |
+| HTML validity errors (W3C nu validator) | /web-validate | Drop from /seo report; note `"see /web-validate report for HTML validity"`. |
+| WCAG accessibility | /web-validate | Drop. |
 | Missing CSP / HSTS / 404 page / HTTP→HTTPS | /harden | Drop unless it directly affects indexability (then mention with cross-link). |
 | Wikidata / sameAs / Knowledge Panel | /seo (GEO) | Owned here. |
 | llms.txt | /seo (GEO) | Owned here. |