Hide immutable type field in color strip source edit modal

Type is set at creation and cannot be changed, so hide the selector
when editing (same pattern already used in value source editor).

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

server/src/wled_controller/static/js/features/color-strips.js

@@ -822,6 +822,9 @@ export async function showCSSEditor(cssId = null, cloneData = null) {
             document.getElementById('css-editor-led-count').value = css.led_count ?? 0;
         };
 
+        // Hide type selector in edit mode (type is immutable)
+        document.getElementById('css-editor-type-group').style.display = cssId ? 'none' : '';
+
         if (cssId) {
             const resp = await fetchWithAuth(`/color-strip-sources/${cssId}`);
             if (!resp.ok) throw new Error('Failed to load color strip source');