feat: add SQL Server connection pool utility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/db.ts

@@ -0,0 +1,22 @@
+import sql from "mssql";
+
+const dbConfig: sql.config = {
+  server: process.env.DB_SERVER!,
+  port: Number(process.env.DB_PORT) || 1433,
+  database: process.env.DB_DATABASE!,
+  user: process.env.DB_USER!,
+  password: process.env.DB_PASSWORD!,
+  options: {
+    encrypt: false,
+    trustServerCertificate: true,
+    enableArithAbort: true,
+  },
+};
+
+let pool: sql.ConnectionPool | null = null;
+
+export async function getPool(): Promise<sql.ConnectionPool> {
+  if (pool && pool.connected) return pool;
+  pool = await sql.connect(dbConfig);
+  return pool;
+}