Fix postgres connection pool leak in development (#195)

In dev mode, viteDevServer.ssrLoadModule re-evaluates server/app.ts on
every request, creating a new postgres connection pool each time and
eventually exhausting Postgres's max_connections limit. Cache the client
on globalThis so HMR re-evaluations reuse the same pool.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

server/app.ts

@@ -13,7 +13,14 @@ export const app = express();
 
 if (!process.env.DATABASE_URL) throw new Error("DATABASE_URL is required");
 
-const client = postgres(process.env.DATABASE_URL);
+// In dev, ssrLoadModule re-evaluates this file on every request. Cache the
+// client on globalThis so HMR re-loads reuse the same connection pool instead
+// of leaking a new one each time.
+declare global {
+  // TypeScript requires `var` in `declare global` blocks — `let`/`const` are not allowed here.
+  var __pgClient: ReturnType<typeof postgres> | undefined; // eslint-disable-line no-var
+}
+const client = (globalThis.__pgClient ??= postgres(process.env.DATABASE_URL));
 const db = drizzle(client, { schema });
 app.use((_, __, next) => DatabaseContext.run(db, next));