Add Drizzle + Postgres setup (task 03)

drizzle-orm + postgres driver + drizzle-kit wired up. Core schema declares
users, households, and household_members. docker-compose.dev.yaml runs
Postgres 16 locally. Initial migration generated and verified applied.

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

src/lib/db.ts

@@ -0,0 +1,6 @@
+import { drizzle } from "drizzle-orm/postgres-js";
+import postgres from "postgres";
+
+const client = postgres(process.env["DATABASE_URL"]!);
+
+export const db = drizzle(client);