feat(auth): add MINDA_DEMO support with auto-seeded demo accounts and username login

frontend/src/features/auth/SetupAndAuthView.tsx

@@ -399,13 +399,44 @@ export const SetupAndAuthView: React.FC<SetupAndAuthViewProps> = ({
 
           {authTab === 'login' && (
             <form onSubmit={handleLogin} className="space-y-3.5">
+              {authStatus.demoMode && (
+                <div className="p-2.5 rounded border border-accent/30 bg-accent/10 space-y-1.5">
+                  <div className="flex items-center justify-between text-[11px] font-semibold text-accent">
+                    <span>🧪 Demo-Modus aktiv</span>
+                    <span className="text-[10px] text-muted font-normal">Klick zum Ausfüllen:</span>
+                  </div>
+                  <div className="flex gap-2">
+                    <button
+                      type="button"
+                      onClick={() => {
+                        setEmail('admin');
+                        setPassword('admin');
+                      }}
+                      className="flex-1 py-1 px-2 text-[11px] rounded bg-panel hover:bg-panel-elevated border border-border text-main font-mono transition-colors text-center"
+                    >
+                      admin / admin
+                    </button>
+                    <button
+                      type="button"
+                      onClick={() => {
+                        setEmail('user');
+                        setPassword('user');
+                      }}
+                      className="flex-1 py-1 px-2 text-[11px] rounded bg-panel hover:bg-panel-elevated border border-border text-main font-mono transition-colors text-center"
+                    >
+                      user / user
+                    </button>
+                  </div>
+                </div>
+              )}
+
               <div>
-                <label className="block text-muted mb-1">E-Mail-Adresse</label>
+                <label className="block text-muted mb-1">Benutzername oder E-Mail-Adresse</label>
                 <input
-                  type="email"
+                  type="text"
                   value={email}
                   onChange={(e) => setEmail(e.target.value)}
-                  placeholder="name@beispiel.de"
+                  placeholder="admin oder name@beispiel.de"
                   required
                   autoFocus
                   className="w-full h-8 px-2.5 input-field"

frontend/src/lib/api.ts

@@ -125,10 +125,10 @@ export const api = {
     return res;
   },
 
-  async login(email: string, password: string): Promise<{ token: string; user: User }> {
+  async login(loginOrEmail: string, password: string): Promise<{ token: string; user: User }> {
     const res = await request<{ token: string; user: User }>('/api/v1/auth/login', {
       method: 'POST',
-      body: JSON.stringify({ email, password }),
+      body: JSON.stringify({ email: loginOrEmail, username: loginOrEmail, login: loginOrEmail, password }),
     });
     setToken(res.token);
     return res;

frontend/src/lib/types.ts

@@ -6,11 +6,13 @@ export interface AuthStatus {
   needsSetup: boolean;
   allowRegistration: boolean;
   instanceName: string;
+  demoMode?: boolean;
 }
 
 export interface User {
   id: string;
   email: string;
+  username?: string;
   displayName: string;
   role: UserRole;
   isActive: boolean;