feat(cart): add loading state management for cart item operations and update payment intent handling

src/app/features/store/pages/checkout-page/checkout-page.component.html

@@ -16,7 +16,7 @@
             [selectedPaymentMethod]="selectedPaymentMethod()"
             [copiedTransferField]="copiedTransferField()"
             [transferAccount]="transferAccount()"
-            [isGeneratingIntent]="isGeneratingIntent()"
+            [isGeneratingIntent]="isPaymentLoading()"
             [qrData]="qrData()"
             (paymentMethodChange)="selectPaymentMethod($event)"
             (copyTransferValue)="copyTransferValue($event.field, $event.value)"

src/app/features/store/pages/checkout-page/checkout-page.component.ts

@@ -1,4 +1,4 @@
-import { ChangeDetectionStrategy, Component, computed, inject, OnInit, signal, ViewChild } from '@angular/core';
+import { ChangeDetectionStrategy, Component, computed, effect, inject, OnInit, signal, untracked, ViewChild } from '@angular/core';
 import { FormBuilder, Validators } from '@angular/forms';
 import { Router } from '@angular/router';
 import { startWith } from 'rxjs';
@@ -80,9 +80,24 @@ export class CheckoutPageComponent implements OnInit {
   protected readonly isCreatingPurchase = signal(false);
   protected readonly createdPurchaseId = signal<number | null>(null);
   protected readonly isGeneratingIntent = signal(false);
+  protected readonly isPaymentLoading = computed(() => this.isGeneratingIntent() || this.cartService.isUpdating());
   protected readonly qrData = signal<string | null>(null);
 
   constructor() {
+    effect(() => {
+      // We only want to trigger the intent generation when the cart changes.
+      // So we track the cart, but untrack the other signals to prevent duplicate calls.
+      const cart = this.cartService.cart();
+      
+      untracked(() => {
+        const purchaseId = this.createdPurchaseId();
+        if (cart && purchaseId) {
+          // Trigger payment intent generation when cart changes and we are on the payment step
+          void this.selectPaymentMethod(this.selectedPaymentMethod());
+        }
+      });
+    });
+
     this.form.statusChanges
       .pipe(startWith(this.form.status))
       .subscribe(() => this.isStep1Valid.set(this.form.valid));