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

CHANGELOG.md

@@ -23,6 +23,7 @@ Format follows [Keep a Changelog](https://keepachangelog.com/).
 - `.claude/{tasks,memory,audits}/` governance layout + 5 memory registries (decisions, learnings, blockers, journal, evals)
 
 ### Changed
+- `/validate` renamed to `/web-validate` — clearer scoped name (W3C + WCAG); routing, skill profiles, cross-references, and the client-deliverable leak-guard updated (the guard still matches legacy `/validate` so older client docs stay covered)
 - `/seo` split into parallel `seo` + `geo` agents with shared resources
 - `/onboard` rewritten: archetype-aware pipeline (orchestrator + config-only agent), security audit archetype-aware
 - `doc-syncer`: stack-aware audit + deploy-doc gating; later scoped to public docs only, `.claude/` read-only; sync-only ROADMAP handling — planned→shipped reconciliation from code/git, never from `.claude/`; numeric incoherence → HUMAN question