fix: replace PrimeVue FloatLabel in WidgetTextarea with CSS-only IFTA label (#9076)

## Summary

Replace PrimeVue `FloatLabel` + `Textarea` in `WidgetTextarea` with a
CSS-only IFTA label and a new shadcn-vue Textarea component, fixing the
label-obscures-content bug.

<img width="965" height="754" alt="image"
src="https://github.com/user-attachments/assets/cab98527-834c-496d-a0ef-942fb21fd862"
/>


## Changes

- **What**: Add `src/components/ui/textarea/Textarea.vue` — thin wrapper
around native `<textarea>` with `cn()` class merging and `defineModel`.
Rewrite `WidgetTextarea.vue` to use a plain `<div>` wrapper with an
absolutely-positioned label and the new Textarea, replacing PrimeVue's
`FloatLabel variant="in"`. Add Storybook stories (Default, Disabled,
WithLabel). Update tests to remove PrimeVue plugin setup.

## Review Focus

- The label uses `absolute left-3 top-1.5 z-10 text-xxs` positioning —
verify it clears textarea content with `pt-5` padding
- `filteredProps` forwards widget options to a native textarea via
`v-bind="restAttrs"` — unknown attrs are silently ignored by the browser

Supersedes #8536

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9076-fix-replace-PrimeVue-FloatLabel-in-WidgetTextarea-with-CSS-only-IFTA-label-30f6d73d3650816fabe5ee30de0c793e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

src/components/ui/textarea/Textarea.stories.ts

@@ -0,0 +1,54 @@
+import type { Meta, StoryObj } from '@storybook/vue3-vite'
+import { ref } from 'vue'
+
+import Textarea from './Textarea.vue'
+
+const meta: Meta<typeof Textarea> = {
+  title: 'UI/Textarea',
+  component: Textarea,
+  tags: ['autodocs']
+}
+
+export default meta
+type Story = StoryObj<typeof Textarea>
+
+export const Default: Story = {
+  render: () => ({
+    components: { Textarea },
+    setup() {
+      const value = ref('Hello world')
+      return { value }
+    },
+    template:
+      '<Textarea v-model="value" placeholder="Type something..." class="max-w-sm" />'
+  })
+}
+
+export const Disabled: Story = {
+  render: () => ({
+    components: { Textarea },
+    template:
+      '<Textarea model-value="Disabled textarea" disabled class="max-w-sm" />'
+  })
+}
+
+export const WithLabel: Story = {
+  render: () => ({
+    components: { Textarea },
+    setup() {
+      const value = ref('Content that sits below the label')
+      return { value }
+    },
+    template: `
+      <div class="relative max-w-sm rounded-lg bg-component-node-widget-background">
+        <label class="pointer-events-none absolute left-3 top-1.5 text-xxs text-muted-foreground z-10">
+          Prompt
+        </label>
+        <Textarea
+          v-model="value"
+          class="size-full resize-none border-none bg-transparent pt-5 text-xs"
+        />
+      </div>
+    `
+  })
+}

src/components/ui/textarea/Textarea.vue

@@ -0,0 +1,24 @@
+<script setup lang="ts">
+import type { HTMLAttributes } from 'vue'
+
+import { cn } from '@/utils/tailwindUtil'
+
+const { class: className, ...restAttrs } = defineProps<{
+  class?: HTMLAttributes['class']
+}>()
+
+const modelValue = defineModel<string | number>()
+</script>
+
+<template>
+  <textarea
+    v-bind="restAttrs"
+    v-model="modelValue"
+    :class="
+      cn(
+        'flex min-h-16 w-full rounded-md border border-input bg-transparent px-3 py-2 text-sm shadow-xs placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50',
+        className
+      )
+    "
+  />
+</template>