fix(brand): link "Runic Gateway" footer badge to Gitea org

Wrap the "Powered by Runic Gateway" wordmark in an anchor pointing to
https://gitea.whitlocktech.com/RunicGateway (new tab, noopener). Adds a
subtle accent-color hover on the wordmark.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XmHdsbnLzDMAVQkAoTQSBe

client/src/components/SiteFooter.jsx

@@ -20,7 +20,14 @@ export default function SiteFooter() {
           <span>
             Powered by
             <br />
-            <strong>Runic Gateway</strong>
+            <a
+              href="https://gitea.whitlocktech.com/RunicGateway"
+              target="_blank"
+              rel="noopener noreferrer"
+              className="site-footer-brand-link"
+            >
+              <strong>Runic Gateway</strong>
+            </a>
           </span>
         </div>
         <div className="site-footer-info">