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/TaxRates/Create.cshtml

@@ -1,4 +1,4 @@
-@model PowderCoating.Core.Entities.TaxRate
+@model PowderCoating.Core.Entities.TaxRate
 @{
     ViewData["Title"] = "Add Tax Rate";
 }
@@ -12,7 +12,7 @@
     <div class="card-body">
         <form asp-action="Create" method="post">
             @Html.AntiForgeryToken()
-            <div asp-validation-summary="ModelOnly" class="alert alert-danger mb-3"></div>
+            <div asp-validation-summary="ModelOnly" class="alert alert-danger alert-permanent mb-3"></div>
 
             <div class="mb-3">
                 <label asp-for="Name" class="form-label fw-semibold">Name <span class="text-danger">*</span></label>

src/PowderCoating.Web/Views/TaxRates/Edit.cshtml

@@ -1,4 +1,4 @@
-@model PowderCoating.Core.Entities.TaxRate
+@model PowderCoating.Core.Entities.TaxRate
 @{
     ViewData["Title"] = "Edit Tax Rate";
 }
@@ -12,7 +12,7 @@
         <form asp-action="Edit" asp-route-id="@Model.Id" method="post">
             @Html.AntiForgeryToken()
             <input type="hidden" asp-for="Id" />
-            <div asp-validation-summary="ModelOnly" class="alert alert-danger mb-3"></div>
+            <div asp-validation-summary="ModelOnly" class="alert alert-danger alert-permanent mb-3"></div>
 
             <div class="mb-3">
                 <label asp-for="Name" class="form-label fw-semibold">Name <span class="text-danger">*</span></label>