feat: add MariaDB schema and connection pool

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/db.js

@@ -0,0 +1,23 @@
+import mariadb from 'mariadb';
+
+let pool;
+
+export function getPool(config) {
+  if (!pool) {
+    pool = mariadb.createPool({
+      host: config.db.host,
+      user: config.db.user,
+      password: config.db.password,
+      database: config.db.database,
+      connectionLimit: 10,
+    });
+  }
+  return pool;
+}
+
+export async function closePool() {
+  if (pool) {
+    await pool.end();
+    pool = undefined;
+  }
+}