docs: Release v1.18.0 documentation

Update all documentation for v1.18.0 release including:
- Add 4 new skills: pdf-creator, claude-md-progressive-disclosurer, promptfoo-evaluation, iOS-APP-developer
- Update marketplace skills count from 23 to 25
- Update version badges and descriptions across README (EN/ZH)
- Update QUICKSTART guides with clearer marketplace install syntax
- Add skill sections with features, use cases, and installation commands
- Update CLAUDE.md with new skill listings and counts
- Update demos index

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

demos/index.html

@@ -548,7 +548,7 @@
             <p>Install the Claude Code Skills Marketplace and start using these skills today!</p>
             <br>
             <p><strong>Quick Install:</strong></p>
-            <p><code>/plugin marketplace add https://github.com/daymade/claude-code-skills</code></p>
+            <p><code>claude plugin marketplace add https://github.com/daymade/claude-code-skills</code></p>
             <br>
             <p>
                 <a href="https://github.com/daymade/claude-code-skills" target="_blank">📖 Documentation</a> |