feat: Implement file upload and management system

- Created database schema for files and file parts.
- Added API endpoint to create a new file and generate an upload token.
- Implemented API endpoint to complete file uploads and generate a download token.
- Developed cron job for cleaning up expired files and deleting associated Discord messages.
- Added API endpoint for soft deletion of files and their parts.
- Implemented API endpoint to fetch file metadata and parts for download.
- Created API endpoint to upload file parts to Discord.
- Developed a client-side download page to handle file decryption and assembly.
- Established database connection pooling for efficient database operations.

src/lib/db.ts

@@ -0,0 +1,17 @@
+import mysql from 'mysql2/promise';
+
+if (!process.env.DB_HOST || !process.env.DB_USER || !process.env.DB_PASSWORD || !process.env.DB_DATABASE) {
+  throw new Error('Please define all database environment variables in .env.local');
+}
+
+const pool = mysql.createPool({
+  host: process.env.DB_HOST,
+  user: process.env.DB_USER,
+  password: process.env.DB_PASSWORD,
+  database: process.env.DB_DATABASE,
+  waitForConnections: true,
+  connectionLimit: 10,
+  queueLimit: 0
+});
+
+export default pool;