fix: Dropdown value must be null (not '') for 'no selection' — was throwing Invalid value

package.json

@@ -1,6 +1,6 @@
 {
   "name": "figma-ai-plugin",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "private": true,
   "dependencies": {
     "@create-figma-plugin/ui": "^4.0.3",

src/ui.tsx

@@ -29,7 +29,7 @@ const MIN_WINDOW_SIZE = { width: 320, height: 200 }
 // very high — actual clamp is done by main via clampWindowSize (bounds*zoom).
 
 // Full plugin version shown in the footer status bar. Keep in sync with package.json "version".
-const PLUGIN_VERSION = '0.1.4'
+const PLUGIN_VERSION = '0.1.5'
 
 const fieldStyle = {
   display: 'flex',
@@ -176,7 +176,7 @@ function SettingsPanel (props: { settings: Settings, setSettings: (s: Settings)
           <div style={{ display: 'flex', gap: 'var(--space-4)', alignItems: 'center' }}>
             <Dropdown
               placeholder={provider.models.length > 0 ? 'Select model' : 'Fetch models first'}
-              value={provider.defaultModel}
+              value={provider.defaultModel === '' ? null : provider.defaultModel}
               onValueChange={function (id: string) { patch({ defaultModel: id }) }}
               options={(provider.models || []).map(function (m) { return { value: m, text: m } })}
             />