feat: New users require admin approval

- Set active=false for newly registered users
- Return RegistrationResponse instead of SessionResponse after registration
- Show success message informing user that admin approval is pending
- Login check already filters for active users only

frontend/src/pages/LoginPage.tsx

@@ -4,6 +4,11 @@ import { apiPost } from "../lib/api";
 import { useSession } from "../lib/session";
 import type { SessionResponse } from "../lib/types";
 
+interface RegistrationResponse {
+  userId: string;
+  email: string;
+}
+
 type FeedbackState =
   | { type: "error"; text: string }
   | { type: "success"; text: string }
@@ -86,14 +91,24 @@ export default function LoginPage() {
       setFeedback(null);
       const { passwordConfirmation, ...registrationPayload } = registration;
       void passwordConfirmation;
-      const response = await apiPost<SessionResponse>("/session/register", registrationPayload);
+      const response = await apiPost<RegistrationResponse>("/session/register", registrationPayload);
       setFeedback({
         type: "success",
-        text: `Registrierung erfolgreich. Willkommen ${response.user.companyName ?? response.user.displayName}.`,
+        text: `Registrierung erfolgreich. Ihr Account (${response.email}) wurde angelegt und muss durch einen Administrator freigegeben werden. Sie werden benachrichtigt, sobald die Freigabe erfolgt ist.`,
       });
-      setSession(response);
-      // Admin zum Dashboard, Kunden zur Startseite
-      navigate(response.user.role === "ADMIN" ? "/admin/dashboard" : "/home");
+      // Reset registration form and switch back to login
+      setRegistration({
+        companyName: "",
+        street: "",
+        houseNumber: "",
+        postalCode: "",
+        city: "",
+        email: "",
+        phoneNumber: "",
+        password: "",
+        passwordConfirmation: "",
+      });
+      setShowRegistration(false);
     } catch (registrationError) {
       setFeedback({ type: "error", text: (registrationError as Error).message });
     }