feat(skill): register seo-signal-validation in marketplace; reconcile spec layout

custom-skills/35-seo-signal-validation/DESIGN.md

@@ -111,16 +111,19 @@ All three call the *same* engine; they differ only in what they compare against.
 
 ```
 35-seo-signal-validation/
-  SKILL.md                 frontmatter (name/description/triggers), mode dispatch,
-                           the cascade, short-circuit + verdict synthesis
-  DESIGN.md                this spec (lives with the skill; no new top-level dir)
-  references/
-    evidence-cascade.md    L1–L4 concrete tool calls + short-circuit rules
-    kg-impact-checks.md     the 5 entity checks incl. Wikidata QID verification
-    verdict-taxonomy.md     conditions + ledger format + narrative template
-    backend-selection.md    pointer to 20/21's existing backend tables (no dup)
+  SKILL.md                 self-contained: classification, 4-layer cascade,
+                           5 KG checks, 4-way verdict, skepticism rules, output
+  DESIGN.md  PLAN.md       spec + plan (live with the skill; no new top-level dir)
+  code/
+    CLAUDE.md              code-environment notes (env, export→script flow)
+    scripts/
+      gsc_signal_delta.py  deterministic L1/L4 GSC delta + mover ranking
+      test_gsc_signal_delta.py
+      requirements.txt     (stdlib only)
 ```
 
+Target environment: Claude Code only (no desktop/ variant — matches precedent 95/96). Registered in .claude-plugin/marketplace.json under ourdigital-seo.
+
 **Triggers:** `validate serp signal`, `is this ranking real`, `prove SEO impact`, `SEMrush surge real?`, `signal validation`, `신호 검증`, `순위 변화 진짜?`, `오가닉 급증 검증`.
 
 **Conventions honored:** no new output directories beyond this approved folder; Notion writes via notion-writer script only; never crawl/audit Marriott for JHR (sameAs reference only); KR deliverables in Korean, English internal notes OK.