Disable zero-LED calibration edges with visual dimming

Edges with 0 LEDs now:
- Dim to 25% opacity (15% for toggle zones)
- Block interaction (pointer-events: none)
- Keep LED input editable to allow changing from 0
- Prevent test toggle, span drag on disabled edges

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/src/wled_controller/static/style.css

@@ -1090,6 +1090,22 @@ input:-webkit-autofill:focus {
     background: rgba(128, 128, 128, 0.25);
 }
 
+.preview-edge.edge-disabled {
+    opacity: 0.25;
+    pointer-events: none;
+}
+
+.preview-edge.edge-disabled .edge-led-input {
+    pointer-events: auto;
+    opacity: 1;
+}
+
+.edge-toggle.edge-disabled {
+    opacity: 0.15;
+    pointer-events: none;
+    cursor: default;
+}
+
 .toggle-top {
     top: -16px;
     left: 56px;