Revert Messages to use /tmp - no write permissions on HF Spaces

- Hugging Face Spaces doesn't allow creating directories in /app
- /tmp works fine for temporary message storage
- Messages reset on rebuilds (acceptable for global chat)

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

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

app/api/messages/route.ts

@@ -2,15 +2,9 @@ import { NextResponse } from 'next/server'
 import fs from 'fs'
 import path from 'path'
 
-// Use persistent storage directory instead of /tmp
-// This ensures messages survive rebuilds and restarts
-const STORAGE_DIR = process.env.PERSISTENT_STORAGE_DIR || path.join(process.cwd(), 'data')
-const dataFilePath = path.join(STORAGE_DIR, 'messages.json')
-
-// Ensure the storage directory exists
-if (!fs.existsSync(STORAGE_DIR)) {
-    fs.mkdirSync(STORAGE_DIR, { recursive: true })
-}
+// Use /tmp for temporary message storage
+// Messages will reset on rebuilds, which is fine for a global chat
+const dataFilePath = path.join('/tmp', 'messages.json')
 
 // Simple bad word list (expand as needed)
 const BAD_WORDS = [