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/styles/theme.css

@@ -1044,6 +1044,13 @@ button[disabled] {
   font-weight: 700;
   letter-spacing: 0.04em;
 }
+.site-footer-brand-link {
+  text-decoration: none;
+  color: inherit;
+}
+.site-footer-brand-link:hover strong {
+  color: var(--accent);
+}
 .site-footer-info {
   display: flex;
   flex-direction: column;