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

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;