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>
     }
 }

src/PowderCoating.Web/wwwroot/js/kiosk-terms.js

@@ -3,21 +3,34 @@
 (function () {
     // ── Signature pad (InPerson sessions only) ─────────────────────────────────
     const canvas = document.getElementById("signatureCanvas");
-    if (canvas) {
+    if (!canvas) return;
+
+    if (typeof SignaturePad === "undefined") {
+        console.error("signature_pad failed to load — signature capture unavailable");
+        canvas.parentElement.insertAdjacentHTML("beforeend",
+            '<p class="text-danger small mt-1">Signature pad failed to load. Please refresh the page.</p>');
+        return;
+    }
+
     const pad = new SignaturePad(canvas, { penColor: "#1e293b" });
 
-        // Scale canvas to device pixel ratio for crisp rendering on high-DPI tablets
+    // Scale canvas to device pixel ratio — must run after layout so offsetWidth is non-zero.
+    // requestAnimationFrame ensures the browser has finished its first layout pass.
     function resizeCanvas() {
         const ratio = Math.max(window.devicePixelRatio || 1, 1);
-            canvas.width  = canvas.offsetWidth  * ratio;
-            canvas.height = canvas.offsetHeight * ratio;
+        const w = canvas.offsetWidth;
+        const h = canvas.offsetHeight;
+        if (w === 0 || h === 0) return;   // layout not ready yet; resize event will retry
+        canvas.width  = w * ratio;
+        canvas.height = h * ratio;
         canvas.getContext("2d").scale(ratio, ratio);
         pad.clear();
     }
-        resizeCanvas();
+
+    requestAnimationFrame(resizeCanvas);
     window.addEventListener("resize", resizeCanvas);
 
-        // Show visual feedback when the canvas has been signed
+    // Visual feedback when the canvas has been signed
     pad.addEventListener("endStroke", function () {
         canvas.classList.add("signed");
     });
@@ -38,11 +51,11 @@
                     const msg = document.getElementById("signatureError");
                     if (msg) msg.classList.remove("d-none");
                     canvas.classList.add("is-invalid");
+                    canvas.scrollIntoView({ behavior: "smooth", block: "center" });
                     return;
                 }
                 hiddenInput.value = pad.toDataURL("image/png");
             }
         });
     }
-    }
 })();