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.Web/Views/Customers/Index.cshtml

@@ -185,12 +185,13 @@
             <div class="mobile-card-view">
                 @if (!Model.Items.Any())
                 {
+                    var isMobileCustomerListFiltered = !string.IsNullOrEmpty(ViewBag.SearchTerm as string);
                     <div class="text-center py-5">
                         <i class="bi bi-inbox" style="font-size: 4rem; color: #d1d5db;"></i>
                         <h5 class="mt-3 text-muted">No customers found</h5>
-                        <p class="text-muted mb-4">@(isCustomerListFiltered ? "No customers match your search." : "Get started by adding your first customer.")</p>
+                        <p class="text-muted mb-4">@(isMobileCustomerListFiltered ? "No customers match your search." : "Get started by adding your first customer.")</p>
                         <a asp-action="Create" class="btn btn-primary">
-                            <i class="bi bi-plus-circle me-2"></i>@(isCustomerListFiltered ? "Add Customer" : "Add Your First Customer")
+                            <i class="bi bi-plus-circle me-2"></i>@(isMobileCustomerListFiltered ? "Add Customer" : "Add Your First Customer")
                         </a>
                     </div>
                 }