feat: add PyPI download stats page with live charts

- Add docs/stats.html with daily download line charts for both packages
- Python version and OS breakdown doughnut charts
- Package comparison table (SDK vs Server vs Combined)
- Live data from pypistats.org API (no build step needed)
- Add Stats link to landing page navigation

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

Author: acailic

docs/index.html

@@ -59,6 +59,7 @@
     <div class="nav-header__links">
       <a href="https://acailic.github.io/agent_debugger/docs/" class="nav-header__link">Docs</a>
       <a href="https://acailic.github.io/agent_debugger/blog/" class="nav-header__link">Blog</a>
+      <a href="https://acailic.github.io/agent_debugger/stats.html" class="nav-header__link">Stats</a>
       <a href="https://github.com/acailic/agent_debugger" class="nav-header__link">GitHub</a>
       <a href="https://pypi.org/project/peaky-peek/" class="nav-header__link">PyPI</a>
     </div>