fix(auth): split login and signup into separate 1Password-compatible forms

1Password showed "No items to display" on the signup password field
because login and registration shared a single form whose password input
switched autocomplete between current-password and new-password, and the
display-name field was dynamically added via v-if. Per 1Password compatible
website design, unrelated flows must be separate forms with stable fields.

Changes:
- Split into two distinct <form> elements: login (autocomplete
  current-password) and signup (autocomplete new-password), each with
  unique field ids so 1Password does not cache the field as a login field
- Add passwordrules, minlength=8, and maxlength=128 to the signup password
  input so 1Password can generate a password matching the server rules
  (min 8 chars)
- Remove the dynamic autocomplete computed and the v-if display-name field;
  each form now has a static, complete field set
- Add .fields form styling (flex column, gap) now that the forms sit inside
  the card container

src/components/AuthModal.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { computed, ref } from 'vue'
+import { ref } from 'vue'
 import { login, oidcLogin, register } from '@/game/auth'
 import { store } from '@/game/store'
 
@@ -10,11 +10,6 @@ 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 = ''
@@ -38,7 +33,7 @@ async function submit(): Promise<void> {
 
 <template>
   <div v-if="store.auth.showAuth" class="backdrop" @click.self="close">
-    <form class="card" @submit.prevent="submit">
+    <div class="card">
       <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>
@@ -48,30 +43,56 @@ async function submit(): Promise<void> {
         <button type="button" :class="{ active: mode === 'register' }" @click="mode = 'register'">Registrieren</button>
       </div>
 
+      <!-- Anmeldung: separates Formular mit current-password -->
+      <form v-if="mode === 'login'" class="fields" @submit.prevent="submit">
         <label class="field">
           <span>Benutzername</span>
-        <input id="username" name="username" v-model="username" maxlength="16" autocomplete="username" />
+          <input id="login-username" name="username" v-model="username" maxlength="16" autocomplete="username" />
         </label>
-      <label v-if="mode === 'register'" class="field">
+        <label class="field">
+          <span>Passwort</span>
+          <input id="login-password" name="password" v-model="password" type="password" autocomplete="current-password" />
+        </label>
+
+        <p v-if="error" class="error">{{ error }}</p>
+
+        <button type="submit" class="primary" :disabled="busy">{{ busy ? '…' : '▶ Anmelden' }}</button>
+      </form>
+
+      <!-- Registrierung: separates Formular mit new-password + Generierungs-Regeln -->
+      <form v-else class="fields" @submit.prevent="submit">
+        <label class="field">
+          <span>Benutzername</span>
+          <input id="register-username" name="username" v-model="username" maxlength="16" autocomplete="username" />
+        </label>
+        <label class="field">
           <span>Anzeigename (optional)</span>
           <input id="displayName" name="displayName" v-model="displayName" maxlength="24" autocomplete="nickname" />
         </label>
         <label class="field">
           <span>Passwort</span>
-        <input id="password" name="password" v-model="password" type="password" :autocomplete="passwordAutocomplete" />
+          <input
+            id="register-password"
+            name="password"
+            v-model="password"
+            type="password"
+            autocomplete="new-password"
+            minlength="8"
+            maxlength="128"
+            passwordrules="minlength: 8; maxlength: 128;"
+          />
         </label>
 
         <p v-if="error" class="error">{{ error }}</p>
 
-      <button type="submit" class="primary" :disabled="busy">
-        {{ busy ? '…' : mode === 'login' ? '▶ Anmelden' : '▶ Konto erstellen' }}
-      </button>
+        <button type="submit" class="primary" :disabled="busy">{{ busy ? '…' : '▶ Konto erstellen' }}</button>
+      </form>
 
       <div v-if="store.auth.oidcEnabled" class="divider"><span>oder</span></div>
       <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>
-    </form>
+    </div>
   </div>
 </template>
 
@@ -138,6 +159,12 @@ h2 {
   color: var(--text);
   border-color: var(--accent);
 }
+.fields {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+  margin: 0;
+}
 .field {
   display: flex;
   flex-direction: column;