Add crew/player/rat name to page title

Each routed page now sets a descriptive document.title so tabs and
browser history entries are distinguishable: the dashboard shows the
Pi-Rat (and human player) name plus crew, the admin panel shows
"Admin · {crew}", the join page is labeled, and home resets to the
app name. New lib/title.js helper composes "{parts} — Rats with Gats".

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

frontend/src/pages/Join.svelte

@@ -1,7 +1,11 @@
 <script>
+    import { onMount } from 'svelte';
     import { push } from 'svelte-spa-router';
     import { apiRequest } from '../lib/api';
+    import { setPageTitle } from '../lib/title';
     export let params = {};
+
+    onMount(() => setPageTitle('Join the Crew'));
     let gameId = params.id;
     let playerName = '';
     let error = '';