Design consistency audit fixes: alerts, cards, dark mode, utilities

Alert sweep (113 alerts, 79 files):
  All persistent static banners now carry alert-permanent so the
  layout's 5-second auto-dismiss cannot swallow guidance, warnings,
  or validation errors. Transient dismissible toasts left untouched.

CSS fixes (site.css):
  .card.shadow-sm      — strips rogue border from ~40 drifted cards
  .card-header.bg-white — rebinds to var(--bs-body-bg) so card
                          headers follow dark/light theme correctly
  Typography utilities  — .text-2xs (.68rem), .text-xs (.73rem)
  Token color classes   — .text-ember, .text-ok, .text-bad,
                          .text-warn, .text-cool, .bg-paper-2
  Layout utilities      — .mw-xs/sm/md/lg replace inline max-width
  Comment              — documents text-ember vs text-primary intent

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

src/PowderCoating.Web/Views/Customers/Details.cshtml

@@ -1,4 +1,4 @@
-@model PowderCoating.Application.DTOs.Customer.CustomerDto
+@model PowderCoating.Application.DTOs.Customer.CustomerDto
 
 @{
     ViewData["Title"] = !string.IsNullOrWhiteSpace(Model.CompanyName)
@@ -123,7 +123,7 @@
                                     }
                                     else
                                     {
-                                        <span class="text-muted">Not set — invoices go to contact email</span>
+                                        <span class="text-muted">Not set — invoices go to contact email</span>
                                     }
                                 </p>
                             </div>
@@ -272,7 +272,7 @@
                             {
                                 <div class="col-md-12">
                                     <label class="text-muted small mb-1">Tax Exempt Certificate</label>
-                                    <div class="alert alert-success d-flex justify-content-between align-items-center mb-0 mt-2">
+                                    <div class="alert alert-success alert-permanent d-flex justify-content-between align-items-center mb-0 mt-2">
                                         <div>
                                             <i class="bi bi-file-earmark-check me-2"></i>
                                             <strong>File on record:</strong> @Model.TaxExemptCertificateFileName
@@ -287,7 +287,7 @@
                             {
                                 <div class="col-md-12">
                                     <label class="text-muted small mb-1">Tax Exempt Certificate</label>
-                                    <div class="alert alert-warning mb-0 mt-2">
+                                    <div class="alert alert-warning alert-permanent mb-0 mt-2">
                                         <i class="bi bi-exclamation-triangle me-2"></i>
                                         <strong>No certificate on file.</strong> Please upload a tax exempt certificate to complete the record.
                                     </div>
@@ -514,7 +514,7 @@
                         <div class="mb-3">
                             <label class="form-label fw-semibold">Reason <span class="text-danger">*</span></label>
                             <select name="Reason" class="form-select" required id="creditReasonSelect">
-                                <option value="">— Select reason —</option>
+                                <option value="">— Select reason —</option>
                                 <option value="Pre-payment / Deposit">Pre-payment / Deposit</option>
                                 <option value="Gift / Gift Card">Gift / Gift Card</option>
                                 <option value="Overpayment credit">Overpayment credit</option>