fix: harden ColorSelect against empty options

`current` was derived as `options.find(...) ?? options[0]`, which is
`undefined` when callers pass an empty array. Subsequent reads of
`current.icon`/`current.label` then crash the render. This was masked
locally (Svelte's reactive runtime swallows the error on some Node
versions) but surfaced as an unhandled error on Node 20 in CI.

Fall back to a placeholder option object so the button still renders.

Author: the0807

webview-ui/src/components/common/ColorSelect.svelte

@@ -21,7 +21,16 @@
   let btnEl: HTMLButtonElement | undefined = $state();
   let dropdownStyle = $state('');
 
-  let current = $derived(options.find(o => o.value === value) ?? options[0]);
+  // Callers can momentarily pass an empty options array — e.g., a parent
+  // component that opens a modal before its store data lands, or a teardown
+  // race where the source list is cleared while the dropdown is still
+  // unmounting. Fall back to a placeholder so the template can render without
+  // crashing on `current.icon` / `current.label`.
+  let current = $derived(
+    options.find(o => o.value === value)
+      ?? options[0]
+      ?? { value: '', label: '', color: '' }
+  );
 
   function toggle() {
     if (open) {