Add simple traffic analytics with source attribution and conversion funnel

- track.js captures first-touch source per session (utm_source/src param
  or external referrer domain) and logs bridge/start page views.
- Join clicks now carry the source; all events aggregate per-source in
  data/analytics.json on the persistent volume.
- Admin: new Traffic & Conversions card with funnel totals (bridge ->
  start -> join click rates) and a per-source breakdown table.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/index.html

@@ -12,4 +12,4 @@
 <section class="section"><div class="wrap"><div class="section-head"><div class="eyebrow">Depth over width</div><h2>2 → 4 → 8 → 16 → 32</h2><p>The first major team milestone is 30 correctly placed positions across the first four generations: 2 + 4 + 8 + 16.</p></div><div class="matrix" aria-label="Matrix growth illustration"><div class="matrix-group"><div class="people"><span class="person"></span><span class="person"></span></div><b>2</b></div><div class="matrix-group"><div class="people"><span class="person"></span><span class="person"></span><span class="person"></span><span class="person"></span></div><b>4</b></div><div class="matrix-group"><div class="people" id="p8"></div><b>8</b></div><div class="matrix-group"><div class="people" id="p16"></div><b>16</b></div></div><div class="notice"><strong>Team principle:</strong> once your two are in place, do not keep adding more directs to the same qualified link. Help the next positions become qualified so the matrix develops depth instead of extra shallow legs.</div></div></section>
 <section class="section"><div class="wrap"><div class="card" style="text-align:center;padding:34px"><div class="eyebrow">Ready to start?</div><h2 style="font-size:38px;margin:10px 0">See the current team placement.</h2><p style="max-width:680px;margin:0 auto 20px;color:var(--muted)">The onboarding page automatically shows the sponsor position the team is currently helping. Always use the sponsor shown there instead of an old screenshot or saved link.</p><a class="btn btn-primary" href="/start">Open Getting Started Instructions →</a></div></div></section>
 </main><footer class="wrap disclaimer">This independent team page is educational and is not an earnings guarantee or investment advice. Cryptocurrency and smart-contract participation involve risk, including possible loss of funds. Never use funds you cannot afford to lose. Results depend on actual participation, qualification, upgrades, smart-contract behavior, and the market value of POL.<div class="footer-links"><a href="/start">Getting Started</a><a href="/admin">Team Admin</a></div></footer>
-<script src="/bridge.js"></script></body></html>
+<script src="/track.js"></script><script src="/bridge.js"></script></body></html>