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

USAGE.md

@@ -111,7 +111,7 @@ Tu veux...
 | Curer la mémoire | `/prune-memory` |
 | Fin de session (= /capitalize --ritual) | `/close` |
 | Audit web (TLS, CSP, headers) | `/harden` |
-| Validité HTML/CSS + a11y | `/validate` |
+| Validité HTML/CSS + a11y | `/web-validate` |
 | Visibilité IA (GEO seul) | `/geo` |
 | Livraison client finale | `/client-handover` |
 | Changer profil skills | `/profile` |
@@ -147,7 +147,7 @@ Tu veux...
 | `/prune-memory` | Registres trop longs / bruyants | Curation : merge, superseded, compression |
 | `/close` | Fin de session | Alias de /capitalize --ritual — dedup + TODO + réflexion 3 questions |
 | `/harden` | Audit sécurité web (SSL, CSP, HSTS) | Projet web avec config HTTP |
-| `/validate` | Audit W3C + WCAG a11y | Avant livraison projet web |
+| `/web-validate` | Audit W3C + WCAG a11y | Avant livraison projet web |
 | `/client-handover` | Livraison client | Audits finaux + livrable brandé |
 | `/profile` | Changer le profil de skills | design / dev / qa / audit / minimal |