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/Registration/Index.cshtml

@@ -1,4 +1,4 @@
-@model PowderCoating.Application.DTOs.Registration.RegisterCompanyDto
+@model PowderCoating.Application.DTOs.Registration.RegisterCompanyDto
 @using PowderCoating.Core.Entities
 
 @{
@@ -309,7 +309,7 @@
 
     @if (!ViewData.ModelState.IsValid && ViewData.ModelState.ErrorCount > 0)
     {
-        <div class="alert alert-danger mb-3">
+        <div class="alert alert-danger alert-permanent mb-3">
             <i class="bi bi-exclamation-triangle-fill me-2"></i>
             <strong>Please fix the errors below:</strong>
             <div asp-validation-summary="All" class="mt-1 mb-0"></div>
@@ -415,7 +415,7 @@
             }
             else
             {
-                <div class="alert alert-warning mt-2" role="alert">
+                <div class="alert alert-warning alert-permanent mt-2" role="alert">
                     <i class="bi bi-exclamation-triangle-fill me-2"></i>
                     No subscription plans are currently available. Please contact a system administrator.
                 </div>