feat: add Storybook stories for WidgetInputText and WidgetTextarea (#9398)

Add Storybook stories for WidgetInputText and WidgetTextarea, aligned
with the Figma Design System spec.

Task: COM-15821

## Summary

Add comprehensive Storybook stories for text widget components and
implement missing Figma design system variants for WidgetInputText.

## Changes

- **WidgetInputText component enhancements**:
- Add `size` prop (`medium` | `large`) matching Figma size variants
(32px / 40px)
- Add `invalid` prop with destructive border style per Figma Invalid
state
- Add `loading` prop showing spinning loader icon per Figma Status state
  - Add hover background (`bg-component-node-widget-background-hovered`)
  - Fix `readonly` not being applied from `widget.options.read_only`
- **WidgetTextarea component fixes**:
  - Show copy button on hover for all states (not just read-only)
  - Apply `text-component-node-foreground` token to copy icon
  - Add hover background to wrapper
- **Storybook stories**:
- WidgetInputText: Default, Disabled, Invalid, Status, WithPlaceholder,
WithLabel stories
- WidgetTextarea: Default, Disabled, HiddenLabel, WithPlaceholder
stories
  - Interactive controls for size, readOnly, disabled, invalid, loading

## Review Focus

- Figma alignment: size/invalid/loading/status variants for
WidgetInputText
- Copy icon color token (`text-component-node-foreground`) for
light/dark theme support
- `layoutWidget` computed pattern to merge `borderStyle` with invalid
state

## Screenshots (if applicable)

<!-- Add screenshots or video recording to help explain your changes -->

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/utils/widgetPropFilter.ts

@@ -17,7 +17,8 @@ export const STANDARD_EXCLUDED_PROPS = [
 export const INPUT_EXCLUDED_PROPS = [
   ...STANDARD_EXCLUDED_PROPS,
   'inputClass',
-  'inputStyle'
+  'inputStyle',
+  'read_only'
 ] as const
 
 export const PANEL_EXCLUDED_PROPS = [