fix(login-i18n): translate the 3 hardcoded JS toasts in customer login

Three more hardcoded English strings in customers/storefront/login.html
were still bypassing i18n because they were emitted from Alpine
showAlert() calls in <script>:

- "Account created successfully! Please sign in." (post-register toast)
- "Login successful! Redirecting..." (post-login toast)
- "Invalid email or password" (login-error fallback)

Same pattern as the earlier forgot/reset-password sweep: defined
window.__customerLoginI18n with `tojson` server-rendered values, read
them once at function entry as `const i18n = ...`, and swapped each
hardcoded string for an i18n property.

Two new auth.* keys × 4 locales (registration_success_signin,
login_success_redirecting). The third reuses the existing
auth.invalid_credentials.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/customers/templates/customers/storefront/login.html

@@ -187,6 +187,15 @@
     <!-- Alpine.js v3 -->
     <script defer src="https://cdn.jsdelivr.net/npm/alpinejs@3.14.0/dist/cdn.min.js"></script>
 
+    {# Translated client-side strings — kept in sync with auth.* keys above #}
+    <script>
+        window.__customerLoginI18n = {
+            registrationSuccess: {{ _('auth.registration_success_signin')|tojson }},
+            loginSuccess: {{ _('auth.login_success_redirecting')|tojson }},
+            invalidCredentials: {{ _('auth.invalid_credentials')|tojson }},
+        };
+    </script>
+
     <!-- Login Logic -->
     <script>
         function languageSelector(currentLang, enabledLanguages) {
@@ -206,6 +215,7 @@
         }
 
         function customerLogin() {
+            const i18n = window.__customerLoginI18n || {};
             return {
                 // Data
                 credentials: {
@@ -234,7 +244,7 @@
                 checkRegistrationSuccess() {
                     const urlParams = new URLSearchParams(window.location.search);
                     if (urlParams.get('registered') === 'true') {
-                        this.showAlert('Account created successfully! Please sign in.', 'success');
+                        this.showAlert(i18n.registrationSuccess, 'success');
                     }
                 },
 
@@ -293,7 +303,7 @@
                         localStorage.setItem('customer_token', data.access_token);
                         localStorage.setItem('customer_user', JSON.stringify(data.user));
 
-                        this.showAlert('Login successful! Redirecting...', 'success');
+                        this.showAlert(i18n.loginSuccess, 'success');
 
                         // Redirect to account page or return URL.
                         // Accepts `?next=` (apiClient's 401-handler convention)
@@ -306,7 +316,7 @@
 
                     } catch (error) {
                         console.error('Login error:', error);
-                        this.showAlert(error.message || 'Invalid email or password');
+                        this.showAlert(error.message || i18n.invalidCredentials);
                     } finally {
                         this.loading = false;
                     }