Fix DXcam engine and improve UI: loading spinners, template card gap

DXcam engine overhaul:
- Remove all user-facing config (device_idx, output_idx, output_color)
  since these are auto-resolved or hardcoded to RGB
- Use one-shot grab() mode with retry for reliability
- Lazily create camera per display via _ensure_camera()
- Clear dxcam global factory cache to prevent stale DXGI state

UI improvements:
- Replace "Loading..." text with CSS spinner animations
- Fix template card header gap on default cards (scope padding-right
  to cards with remove button only via :has selector)
- Add auto-restart server rule to CLAUDE.md

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

server/src/wled_controller/static/style.css

@@ -165,7 +165,8 @@ section {
     gap: 20px;
 }
 
-.devices-grid > .loading {
+.devices-grid > .loading,
+.devices-grid > .loading-spinner {
     grid-column: 1 / -1;
 }
 
@@ -735,6 +736,27 @@ input:-webkit-autofill:focus {
     color: #999;
 }
 
+.loading-spinner {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    padding: 40px;
+}
+
+.loading-spinner::after {
+    content: '';
+    width: 28px;
+    height: 28px;
+    border: 3px solid var(--border-color);
+    border-top-color: var(--primary-color);
+    border-radius: 50%;
+    animation: spin 0.8s linear infinite;
+}
+
+@keyframes spin {
+    to { transform: rotate(360deg); }
+}
+
 /* Full-page overlay spinner */
 .overlay-spinner {
     position: fixed;
@@ -1815,6 +1837,9 @@ input:-webkit-autofill:focus {
     justify-content: space-between;
     align-items: center;
     margin-bottom: 12px;
+}
+
+.template-card:has(.card-remove-btn) .template-card-header {
     padding-right: 24px;
 }