feat(ui): player stats modal and admin button for ADMIN_USERS accounts

The admin dashboard exposed account stats, but players had no way to see
their own. Both gaps are closed:

Player stats modal (src/components/PlayerStats.vue):
- New "📊 Statistik" chip in the profile bar, available to logged-in
  players AND guests (guest progress lives in the same profile shape)
- Shows crystals, rounds played, wins incl. win rate, kills, total score,
  best wave, and a research progress bar (owned vs. total upgrade levels)
- Guests get a hint that their progress is local-only and transfers into
  an account on first login

Admin shortcut:
- Logged-in users whose account is listed in ADMIN_USERS (server already
  sets publicUser.admin) now get a "🛡️ Admin" chip in the profile bar
  that links to /admin with the existing session
- UserMetaProfile type gains the optional admin flag

Verified in the browser: guest sees the stats button but no admin chip;
after logging in as an ADMIN_USERS account the admin chip appears and
navigates to the dashboard (data loads, 1 account). Build clean, 54/54
tests green.

src/components/UserProfileBar.vue

@@ -5,13 +5,20 @@ import { store } from '@/game/store'
 
 const user = computed(() => store.auth.user)
 const loggedIn = computed(() => !!user.value && user.value.id !== 'guest')
+const isAdmin = computed(() => Boolean(user.value?.admin))
 
 function openResearch(): void {
   store.auth.showResearch = true
 }
+function openStats(): void {
+  store.auth.showStats = true
+}
 function openAuth(): void {
   store.auth.showAuth = true
 }
+function openAdmin(): void {
+  window.location.href = '/admin'
+}
 async function doLogout(): Promise<void> {
   await logout()
 }
@@ -24,11 +31,14 @@ async function doLogout(): Promise<void> {
     </div>
     <template v-if="loggedIn">
       <span class="name" :title="user?.username">👤 {{ user?.displayName }}</span>
+      <button class="chip stats" @click="openStats">📊 Statistik</button>
       <button class="chip research" @click="openResearch">🧪 Forschung</button>
+      <button v-if="isAdmin" class="chip admin" title="Admin-Dashboard öffnen" @click="openAdmin">🛡️ Admin</button>
       <button class="chip" @click="doLogout">Abmelden</button>
     </template>
     <template v-else>
       <span class="name">👤 Gast</span>
+      <button class="chip stats" @click="openStats">📊 Statistik</button>
       <button class="chip research" @click="openResearch">🧪 Forschung</button>
       <button class="chip login" @click="openAuth">Anmelden</button>
     </template>
@@ -75,6 +85,13 @@ async function doLogout(): Promise<void> {
 .chip.research {
   border-color: #3d6f9e;
 }
+.chip.stats {
+  border-color: #6e5a9e;
+}
+.chip.admin {
+  border-color: #9e503d;
+  color: #ffb0a0;
+}
 .chip.login {
   border-color: #3f8f37;
   color: #b8e6b0;