fix(auth): make login/signup fields password-manager friendly

Password managers (1Password, Bitwarden, …) could not reliably detect or
fill the auth fields because the inputs were loose labels inside a div with
no real form, no name attributes, and a static autocomplete hint.

Changes:
- Wrap the auth card in a real <form @submit.prevent> so password managers
  recognize the credential form and its submit flow
- Add id/name attributes to all fields (username, displayName, password)
- Use a dynamic autocomplete hint on the password field:
  current-password for login (autofill) and new-password for registration
  (offer a generated strong password)
- Set autocomplete="nickname" on the display-name field so it is not
  mistaken for a username or password field
- Mark the close, tab-switch, and OIDC buttons as type="button" so they no
  longer default to type="submit" and trigger form submission
- Make the primary action a type="submit" button so Enter submits natively
- Add margin: 0 to .card since it is now a form element

src/components/AuthModal.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref } from 'vue'
+import { computed, ref } from 'vue'
 import { login, oidcLogin, register } from '@/game/auth'
 import { store } from '@/game/store'
 
@@ -10,6 +10,11 @@ const displayName = ref('')
 const busy = ref(false)
 const error = ref('')
 
+// Password managers (1Password, Bitwarden, …) rely on distinct autocomplete
+// hints: "current-password" for login, "new-password" so a strong password is
+// suggested/saved during registration.
+const passwordAutocomplete = computed(() => (mode.value === 'login' ? 'current-password' : 'new-password'))
+
 function close(): void {
   store.auth.showAuth = false
   error.value = ''
@@ -33,40 +38,40 @@ async function submit(): Promise<void> {
 
 <template>
   <div v-if="store.auth.showAuth" class="backdrop" @click.self="close">
-    <div class="card">
-      <button class="close" @click="close">✕</button>
+    <form class="card" @submit.prevent="submit">
+      <button type="button" class="close" @click="close">✕</button>
       <h2>{{ mode === 'login' ? 'Anmelden' : 'Konto erstellen' }}</h2>
       <p class="sub">Speichere Kristalle, Forschung & Statistiken über alle Runden hinweg.</p>
 
       <div class="tabs">
-        <button :class="{ active: mode === 'login' }" @click="mode = 'login'">Anmelden</button>
-        <button :class="{ active: mode === 'register' }" @click="mode = 'register'">Registrieren</button>
+        <button type="button" :class="{ active: mode === 'login' }" @click="mode = 'login'">Anmelden</button>
+        <button type="button" :class="{ active: mode === 'register' }" @click="mode = 'register'">Registrieren</button>
       </div>
 
       <label class="field">
         <span>Benutzername</span>
-        <input v-model="username" maxlength="16" autocomplete="username" @keyup.enter="submit" />
+        <input id="username" name="username" v-model="username" maxlength="16" autocomplete="username" />
       </label>
       <label v-if="mode === 'register'" class="field">
         <span>Anzeigename (optional)</span>
-        <input v-model="displayName" maxlength="24" @keyup.enter="submit" />
+        <input id="displayName" name="displayName" v-model="displayName" maxlength="24" autocomplete="nickname" />
       </label>
       <label class="field">
         <span>Passwort</span>
-        <input v-model="password" type="password" autocomplete="current-password" @keyup.enter="submit" />
+        <input id="password" name="password" v-model="password" type="password" :autocomplete="passwordAutocomplete" />
       </label>
 
       <p v-if="error" class="error">{{ error }}</p>
 
-      <button class="primary" :disabled="busy" @click="submit">
+      <button type="submit" class="primary" :disabled="busy">
         {{ busy ? '…' : mode === 'login' ? '▶ Anmelden' : '▶ Konto erstellen' }}
       </button>
 
       <div v-if="store.auth.oidcEnabled" class="divider"><span>oder</span></div>
-      <button v-if="store.auth.oidcEnabled" class="oidc" @click="oidcLogin">🔑 {{ store.auth.oidcLabel }}</button>
+      <button type="button" v-if="store.auth.oidcEnabled" class="oidc" @click="oidcLogin">🔑 {{ store.auth.oidcLabel }}</button>
 
       <p class="hint">Als Gast spielen? Einfach schließen – Fortschritt wird lokal gespeichert.</p>
-    </div>
+    </form>
   </div>
 </template>
 
@@ -83,6 +88,7 @@ async function submit(): Promise<void> {
 }
 .card {
   position: relative;
+  margin: 0;
   background: var(--panel);
   border: 1px solid var(--panel-border);
   border-radius: 16px;