feat(panel): rename Account to Settings

The nav entry, page heading, and browser title now read Settings. The
route, template name, and Active key stay `account`, so existing links
and bookmarks keep working.

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

internal/web/templates/account.html

@@ -1,5 +1,5 @@
 {{define "content"}}
-<h1>Account</h1>
+<h1>Settings</h1>
 
 {{if .Flash}}<div class="flash">{{.Flash}}</div>{{end}}