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/harden/SKILL.md

@@ -352,8 +352,8 @@ Agent(
     - Legal pages (mentions légales, CGV, privacy) — unless the issue is
       a security-header gap on those pages, not their content
     - Content quality, keyword density, readability
-    - a11y / WCAG (owned by /validate — W3C + WCAG audit)
-    - W3C HTML / CSS syntactic validity (owned by /validate)
+    - a11y / WCAG (owned by /web-validate — W3C + WCAG audit)
+    - W3C HTML / CSS syntactic validity (owned by /web-validate)
 
   If you detect an out-of-scope issue, DROP IT silently. Do NOT mention
   it even as a "note". Stay focused.