feat: migrate from @iconify/tailwind to @iconify/tailwind4 (#8724)

## Summary

Migrate from `@iconify/tailwind` (Tailwind 3 JS plugin) to
`@iconify/tailwind4` (native Tailwind 4 CSS plugin), moving all config
into CSS directives.

## Changes

- **What**: Replace `addDynamicIconSelectors()` JS plugin with `@plugin
"@iconify/tailwind4"` CSS directive. Move `boxShadow` theme extension
into `@theme` block. Delete both `tailwind.config.ts` files and the
runtime `iconCollection.ts` module.
- **Dependencies**: `@iconify/tailwind` removed, `@iconify/tailwind4`
added

## Review Focus

- `from-folder` path resolution in monorepo context (paths relative to
project root)
- SVG auto-cleanup behavior of `from-folder` vs the previous manual
`iconCollection.ts` loader
- Removal of `@config` directive and both tailwind config files — all
config now in CSS

## Files

| File | Change |
|------|--------|
| `pnpm-workspace.yaml` | Swap catalog entry |
| `packages/design-system/package.json` | Swap dep, remove
`tailwind-config` export |
| `packages/design-system/src/css/style.css` | Add `@plugin`,
`--shadow-interface` theme token, remove `@config` |
| `packages/design-system/tailwind.config.ts` | Deleted |
| `packages/design-system/src/iconCollection.ts` | Deleted |
| `tailwind.config.ts` | Deleted |
| `tsconfig.json`, `components.json` | Remove stale references |
| `knip.config.ts` | Ignore `@iconify-json/lucide` (CSS-consumed, not
JS-imported) |
| Docs | Updated `CONTRIBUTING.md` and `icons/README.md` |

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8724-feat-migrate-from-iconify-tailwind-to-iconify-tailwind4-3006d73d36508144a9b3e7ae73448f98)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

packages/design-system/src/icons/README.md

@@ -251,26 +251,25 @@ Icons are automatically imported using `unplugin-icons` - no manual imports need
 
 The icon system has two layers:
 
-1. **Build-time Processing** (`packages/design-system/src/iconCollection.ts`):
-   - Scans `packages/design-system/src/icons/` for SVG files
-   - Validates SVG content and structure
-   - Creates Iconify collection for Tailwind CSS
-   - Provides error handling for malformed files
+1. **Tailwind CSS Plugin** (`@iconify/tailwind4`):
+   - Configured via `@plugin` directive in `packages/design-system/src/css/style.css`
+   - Uses `from-folder(comfy, ...)` to load SVGs from `packages/design-system/src/icons/`
+   - Auto-cleans and optimizes SVGs at build time
 
 2. **Vite Runtime** (`vite.config.mts`):
    - Enables direct SVG import as Vue components
    - Supports dynamic icon loading
 
-```typescript
-// Build script creates Iconify collection
-export const iconCollection: IconifyCollection = {
-  prefix: 'comfy',
-  icons: {
-    workflow: { body: '<svg>...</svg>' },
-    node: { body: '<svg>...</svg>' }
-  }
+```css
+/* CSS configuration for Tailwind icon classes */
+@plugin "@iconify/tailwind4" {
+  prefix: 'icon';
+  scale: 1.2;
+  icon-sets: from-folder(comfy, './packages/design-system/src/icons');
 }
+```
 
+```typescript
 // Vite configuration for component-based usage
 Icons({
   compiler: 'vue3',