Add QuoteApprovedByCustomer notification type; fix wrong type logged on approval

QuoteDeclinedByCustomer was used for both approve and decline responses,
so approval notifications showed the wrong type in the log. Added a distinct
QuoteApprovedByCustomer = 16 enum value, wired up the correct type in
NotificationService, added default templates in both the service fallback
dictionary and SeedData, and updated placeholder hints in CompanySettings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Infrastructure/Data/SeedData.cs

@@ -977,6 +977,28 @@ New accounts walk through an 18-step setup wizard to configure company informati
                 CompanyId = companyId,
                 CreatedAt = DateTime.UtcNow
             },
+            new NotificationTemplate
+            {
+                NotificationType = NotificationType.QuoteApprovedByCustomer,
+                Channel = NotificationChannel.Email,
+                DisplayName = "Quote Approved by Customer (Internal)",
+                Subject = "Customer Response: Quote {{quoteNumber}} — {{companyName}}",
+                Body = "<p>Hello,</p><p>A customer has responded to quote <strong>{{quoteNumber}}</strong>.</p><p><strong>Customer:</strong> {{customerName}}<br/><strong>Response:</strong> {{response}}</p><p>Log in to the portal to review and follow up.</p>",
+                IsActive = true,
+                CompanyId = companyId,
+                CreatedAt = DateTime.UtcNow
+            },
+            new NotificationTemplate
+            {
+                NotificationType = NotificationType.QuoteDeclinedByCustomer,
+                Channel = NotificationChannel.Email,
+                DisplayName = "Quote Declined by Customer (Internal)",
+                Subject = "Customer Response: Quote {{quoteNumber}} — {{companyName}}",
+                Body = "<p>Hello,</p><p>A customer has responded to quote <strong>{{quoteNumber}}</strong>.</p><p><strong>Customer:</strong> {{customerName}}<br/><strong>Response:</strong> {{response}}</p>{{declineReasonSection}}<p>Log in to the portal to review and follow up.</p>",
+                IsActive = true,
+                CompanyId = companyId,
+                CreatedAt = DateTime.UtcNow
+            },
         ];
     }