fix(marketplace): replace the dead Discord invite (#65)

The marketplace footer linked discord.gg/9JWNpH7E, which returns 404 from the
Discord API. It now links grgzFEHgkj, the invite the quickstart already uses.


Claude-Session: https://claude.ai/code/session_013aK3gVWzNdcM3hZ2o2awK2

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: imran-siddique

marketplace/index.html

@@ -24,7 +24,7 @@
   </div></section>
   <section class="market-submit"><div class="wrap submit-grid"><div><p class="eyebrow">Make the ecosystem bigger</p><h2>Your integration belongs here.</h2></div><div><p>Connect a framework, platform, policy engine, or governance product to the AgenTrust stack. The submission path is public, self-serve, and governed by the same rules for everyone.</p><a class="button primary" href="https://github.com/agentrust-io/integrations/blob/main/CONTRIBUTING.md">List your integration ↗</a></div></div></section>
 </main>
-<footer class="site-footer"><div class="wrap foot-in"><div class="foot-brand"><a class="wordmark" href="/">agentrust<span>.</span>io</a><p class="tagline">Open infrastructure for verifiable AI agents.</p></div><div class="foot-links"><a href="https://github.com/agentrust-io">GitHub</a><a href="https://discord.gg/9JWNpH7E">Discord</a><a href="/">Ecosystem</a></div></div><div class="wrap foot-legal">Marketplace listings describe technical integrations, not endorsement, certification, or commercial availability.</div></footer>
+<footer class="site-footer"><div class="wrap foot-in"><div class="foot-brand"><a class="wordmark" href="/">agentrust<span>.</span>io</a><p class="tagline">Open infrastructure for verifiable AI agents.</p></div><div class="foot-links"><a href="https://github.com/agentrust-io">GitHub</a><a href="https://discord.gg/grgzFEHgkj">Discord</a><a href="/">Ecosystem</a></div></div><div class="wrap foot-legal">Marketplace listings describe technical integrations, not endorsement, certification, or commercial availability.</div></footer>
 <script src="/hub-nav.js"></script>
 <script src="/marketplace/marketplace.js?v=5"></script>
 </body></html>