Fix NoExtraLayerCharge persistence, appointment reminders, coat notes display, scroll restoration, and invoice Send dead-button

- Appointment reminders: add AppointmentReminderBackgroundService (60s poll), ReminderSentAt
  dedup stamp, NotifyAppointmentReminderAsync sends both customer email and creator staff email;
  AppointmentReminderStaff notification type + default template added; DateTime.Now used instead
  of UtcNow to match locally-stored ScheduledStartTime; ToLocalTime() double-conversion removed

- NoExtraLayerCharge not persisted: flag existed on CreateQuoteItemCoatDto and was used by
  pricing engine but never written to JobItemCoat/QuoteItemCoat entities — every edit reset it
  to false and re-applied the extra layer charge; added column to both entities (migration
  AddNoExtraLayerChargeToCoats), both read DTOs, all 3 JobItemAssemblyService overloads,
  JobItemCoatSeed inner class, and existingItemsData JSON in all 5 wizard views; fixed JS
  template path that hard-coded noExtraLayerCharge: false

- Coat notes not visible: notes were rendered in desktop job details but missing from the wizard
  item card summary and the mobile card view; both fixed

- Scroll position lost on item save: sessionStorage save/restore added to item-wizard.js owner
  form submit handler; path-keyed so cross-page navigation does not restore stale position;
  requestAnimationFrame used for reliable mobile scroll restoration

- Invoice Send dead button: #sendChannelModal was gated inside @if (isDraft) but the button
  targeting it fires for Sent/Overdue invoices too when customer has both email and SMS; modal
  moved outside the Draft guard

- InitialCreate migration added for fresh database installs; Baseline migration guarded with
  IF OBJECT_ID check so it no-ops on fresh DBs; Razor scoping bug fixed in Customers/Index.cshtml

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

src/PowderCoating.Application/Interfaces/INotificationService.cs

@@ -91,4 +91,11 @@ public interface INotificationService
     /// Alert company staff when a Stripe chargeback (dispute) is opened on an invoice payment.
     /// </summary>
     Task NotifyChargebackAlertAsync(Invoice invoice, string disputeId, decimal amount, string reason);
+
+    /// <summary>
+    /// Sends an appointment reminder email to the linked customer (if opted in) and writes a
+    /// notification log row. Called by <see cref="PowderCoating.Web.BackgroundServices.AppointmentReminderBackgroundService"/>
+    /// when the reminder window opens. In-app bell notification is handled by the caller.
+    /// </summary>
+    Task NotifyAppointmentReminderAsync(Appointment appointment);
 }