Fix kiosk signature pad: host locally, fix canvas resize timing

- Download signature_pad 4.1.7 to wwwroot/lib/signature-pad/ to eliminate
  CDN SRI hash failures and network dependencies on the tablet
- Wrap resizeCanvas in requestAnimationFrame so offsetWidth is non-zero
  when measured (browser layout pass must complete first)
- Add guard for SignaturePad not defined (shows user-visible error instead
  of silent JS crash)
- Add scrollIntoView on signature validation error for better tablet UX

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

src/PowderCoating.Web/Views/Kiosk/Intake/Terms.cshtml

@@ -90,9 +90,7 @@
 @if (isInPerson)
 {
     @section Scripts {
-        <script src="https://cdn.jsdelivr.net/npm/signature_pad@4.1.7/dist/signature_pad.umd.min.js"
-                integrity="sha384-bQMMRVcRi5vEIBLKnB4FY7tBOA9k/Qvd/9zSWMNO4h0zfB2qLj4DV2R/JyPAbF3"
-                crossorigin="anonymous"></script>
+        <script src="~/lib/signature-pad/signature_pad.umd.min.js"></script>
         <script src="~/js/kiosk-terms.js"></script>
     }
 }