feat: add comprehensive loading feedback (#18)

frontend/src/app/components/apartment-form/apartment-form.ts

@@ -3,16 +3,25 @@ import { FormsModule } from '@angular/forms';
 import { MatButtonModule } from '@angular/material/button';
 import { MatFormFieldModule } from '@angular/material/form-field';
 import { MatInputModule } from '@angular/material/input';
+import { MatProgressSpinnerModule } from '@angular/material/progress-spinner';
 import { Apartment } from '../../services/apartment.service';
 
 @Component({
   selector: 'app-apartment-form',
-  imports: [FormsModule, MatButtonModule, MatFormFieldModule, MatInputModule],
+  imports: [
+    FormsModule,
+    MatButtonModule,
+    MatFormFieldModule,
+    MatInputModule,
+    MatProgressSpinnerModule,
+  ],
   templateUrl: './apartment-form.html',
   styleUrl: './apartment-form.css',
 })
 export class ApartmentForm {
   readonly apartment = input<Apartment | null>(null);
+  readonly saving = input(false);
+  readonly saveError = input('');
   readonly closed = output<void>();
   readonly saved = output<Apartment>();
 
@@ -27,6 +36,7 @@ export class ApartmentForm {
   }
 
   save(): void {
+    if (this.saving()) return;
     if (!this.name().trim() || !this.address().trim() || this.purchasePrice() <= 0) {
       this.error.set('Veuillez remplir tous les champs obligatoires (Nom, Adresse, Prix > 0).');
       return;