chore: replace manual SQL migrations with node-pg-migrate

backend/migrate.js

@@ -0,0 +1,27 @@
+const { runner } = require('node-pg-migrate');
+const path = require('path');
+
+const direction = process.argv[2] || 'up';
+
+runner({
+  databaseUrl: {
+    host: process.env.PGHOST || 'localhost',
+    port: parseInt(process.env.PGPORT || '5432', 10),
+    user: process.env.PGUSER,
+    password: process.env.PGPASSWORD,
+    database: process.env.PGDATABASE
+  },
+  dir: path.resolve(__dirname, 'migrations'),
+  direction,
+  migrationsTable: 'pgmigrations',
+  count: direction === 'down' ? 1 : Infinity,
+  log: (msg) => console.log(msg)
+})
+  .then((applied) => {
+    console.log(`Migration complete — ${applied.length} migration(s) ${direction === 'down' ? 'reverted' : 'applied'}.`);
+    process.exit(0);
+  })
+  .catch((err) => {
+    console.error('Migration failed:', err.message);
+    process.exit(1);
+  });