update: rebrand Vert to Convert with improved description

- Rename tool from "Vert" to "Convert" across all files
- Update URL: vert.kit.pivoine.art → convert.kit.pivoine.art
- Improve description to highlight WebAssembly technology
- Update metadata keywords from 'vert' to 'convert'
- Better reflect actual features: videos, images, and audio conversion

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/layout.tsx

@@ -4,7 +4,7 @@ import './globals.css';
 export const metadata: Metadata = {
   title: 'Kit - Your Creative Toolkit',
   description: 'A curated collection of creative and utility tools for developers and creators. Features file conversion, image editing, and color manipulation.',
-  keywords: ['tools', 'utilities', 'file converter', 'image editor', 'color palette', 'creative toolkit', 'vert', 'paint', 'pastel', 'open source'],
+  keywords: ['tools', 'utilities', 'file converter', 'image editor', 'color palette', 'creative toolkit', 'convert', 'paint', 'pastel', 'open source'],
   authors: [{ name: 'pivoine.art' }],
   creator: 'pivoine.art',
   publisher: 'pivoine.art',