docs: integrate x-twitter-growth across plugin ecosystem and documentation

- Sync Gemini CLI (208 items), verify Codex CLI (151 skills)
- Update marketplace.json: 151 packages, marketing 43, tools 245
- Update marketing plugin.json with X/Twitter growth, 43 skills
- Update CLAUDE.md, README.md, docs/index.md, getting-started.md counts
  (172 skills, 245 tools, 344 references)
- Add x-twitter-growth to marketing CLAUDE.md skill map
- Add x-twitter-growth docs page and mkdocs.yml nav entry
- Regenerate 207 MkDocs pages, build verified

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

.gemini/skills-index.json

@@ -1,7 +1,7 @@
 {
   "version": "1.0.0",
   "name": "gemini-cli-skills",
-  "total_skills": 207,
+  "total_skills": 208,
   "skills": [
     {
       "name": "cs-agile-product-owner",
@@ -893,6 +893,11 @@
       "category": "marketing",
       "description": "When the user wants to develop social media strategy, plan content calendars, manage community engagement, or grow their social presence across platforms. Also use when the user mentions 'social media strategy,' 'social calendar,' 'community management,' 'social media plan,' 'grow followers,' 'engagement rate,' 'social media audit,' or 'which platforms should I use.' For writing individual social posts, see social-content. For analyzing social performance data, see social-media-analyzer."
     },
+    {
+      "name": "x-twitter-growth",
+      "category": "marketing",
+      "description": "X/Twitter growth engine for building audience, crafting viral content, and analyzing engagement. Use when the user wants to grow on X/Twitter, write tweets or threads, analyze their X profile, research competitors on X, plan a posting strategy, or optimize engagement. Complements social-content (generic multi-platform) with X-specific depth: algorithm mechanics, thread engineering, reply strategy, profile optimization, and competitive intelligence via web search."
+    },
     {
       "name": "agile-product-owner",
       "category": "product",
@@ -1069,7 +1074,7 @@
       "description": "Finance resources"
     },
     "marketing": {
-      "count": 43,
+      "count": 44,
       "description": "Marketing resources"
     },
     "product": {

.gemini/skills/x-twitter-growth/SKILL.md

@@ -0,0 +1 @@
+../../../marketing-skill/x-twitter-growth/SKILL.md