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>

docs/guide.md

@@ -223,7 +223,7 @@ service healthy and will mail be accepted?"
 - **Backup** (`/backup`) — download a full-server backup; the same page hosts
   the domain-import form (`POST /domains/import`). See
   [Backup, restore, and moving a single domain](#backup-restore-and-moving-a-single-domain).
-- **Account** (`/account`) — change the administrator username and/or password.
+- **Settings** (`/account`) — change the administrator username and/or password.
   Application SASL logins are separate and are not changed here.
 
 **Sessions.** A login survives a container restart: sessions live in SQLite, not