feat: add payment_orders table migration

migrations/002_add_payment_orders.sql

@@ -0,0 +1,15 @@
+-- migrations/002_add_payment_orders.sql
+CREATE TABLE IF NOT EXISTS payment_orders (
+    id           SERIAL PRIMARY KEY,
+    user_id      INTEGER NOT NULL REFERENCES users(id),
+    order_no     VARCHAR(64) UNIQUE NOT NULL,
+    package_type VARCHAR(20) NOT NULL,
+    amount       INTEGER NOT NULL,
+    status       VARCHAR(20) NOT NULL DEFAULT 'pending',
+    paid_at      TIMESTAMPTZ,
+    expires_at   TIMESTAMPTZ,
+    created_at   TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_payment_orders_user_id ON payment_orders(user_id);
+CREATE INDEX IF NOT EXISTS idx_payment_orders_order_no ON payment_orders(order_no);