feat(docker): production-ready Dockerfile + Portainer compose stack

- Rewrite Dockerfile: multi-stage pnpm monorepo build with Next.js
  standalone output, non-root user, minimal runner image
- Enable next.config.ts `output: standalone` + serverExternalPackages
- Rewrite docker/compose.prod.yml: full production stack with migrate
  service, minio-init, named networks, build context for Portainer
- Add scripts/migrate.mjs: standalone Drizzle migration runner
- Update .dockerignore for cleaner build context

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

scripts/migrate.mjs

@@ -0,0 +1,18 @@
+import { drizzle } from "drizzle-orm/node-postgres";
+import { migrate } from "drizzle-orm/node-postgres/migrator";
+import pg from "pg";
+
+const { Pool } = pg;
+const pool = new Pool({ connectionString: process.env.DATABASE_URL });
+const db = drizzle(pool);
+
+try {
+  await migrate(db, { migrationsFolder: "/app/packages/db/src/migrations" });
+  console.log("Migrations applied successfully");
+  await pool.end();
+  process.exit(0);
+} catch (err) {
+  console.error("Migration failed:", err);
+  await pool.end().catch(() => {});
+  process.exit(1);
+}