Restructure skill numbering: SEO 11-30, GTM 60-69, reserve 19-28 for future skills

Renumber 12 existing skills to new ranges:
- SEO: 11→13, 12→18, 13→16, 14→17, 15→14, 16→15, 17→29, 18→30, 19→12
- GTM: 20→60, 21→61, 22→62

Update cross-references in gateway architect/builder skills, GTM guardian
README, CLAUDE.md (skill tables + directory layout), and AGENTS.md
(domain routing ranges).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

custom-skills/13-seo-on-page-audit/desktop/tools/firecrawl.md

@@ -0,0 +1,15 @@
+# Firecrawl
+
+> TODO: Document tool usage for this skill
+
+## Available Commands
+
+- [ ] List commands
+
+## Configuration
+
+- [ ] Add configuration details
+
+## Examples
+
+- [ ] Add usage examples

custom-skills/13-seo-on-page-audit/desktop/tools/notion.md

@@ -0,0 +1,15 @@
+# Notion
+
+> TODO: Document tool usage for this skill
+
+## Available Commands
+
+- [ ] List commands
+
+## Configuration
+
+- [ ] Add configuration details
+
+## Examples
+
+- [ ] Add usage examples

custom-skills/13-seo-on-page-audit/desktop/tools/perplexity.md

@@ -0,0 +1,15 @@
+# Perplexity
+
+> TODO: Document tool usage for this skill
+
+## Available Commands
+
+- [ ] List commands
+
+## Configuration
+
+- [ ] Add configuration details
+
+## Examples
+
+- [ ] Add usage examples