feat: add local PostgreSQL via docker-compose and devenv

Two options for running Postgres locally:

1. Docker Compose: `docker compose up -d` starts a PostgreSQL 17
container on port 5432 with persistent volume storage.

2. Devenv: `devenv up` now also starts a managed PostgreSQL 17 service
alongside the appview and web dev servers.

Both use the same credentials (atbb/atbb) and database name (atbb),
matching the existing DATABASE_URL in .env.example.

https://claude.ai/code/session_01T1qT4qo8eoui9X7f32PVt4

devenv.nix

···
     pkgs.turbo
   ];
 
+  services.postgres = {
+    enable = true;
+    package = pkgs.postgresql_17;
+    listen_addresses = "127.0.0.1";
+    port = 5432;
+    initialDatabases = [
+      { name = "atbb"; }
+    ];
+    initialScript = ''
+      CREATE USER atbb WITH PASSWORD 'atbb';
+      GRANT ALL PRIVILEGES ON DATABASE atbb TO atbb;
+      ALTER DATABASE atbb OWNER TO atbb;
+    '';
+  };
+
   processes = {
     appview.exec = "pnpm --filter @atbb/appview dev";
     web.exec = "pnpm --filter @atbb/web dev";

docker-compose.yml

···
+services:
+  postgres:
+    image: postgres:17
+    container_name: atbb-postgres
+    environment:
+      POSTGRES_USER: atbb
+      POSTGRES_PASSWORD: atbb
+      POSTGRES_DB: atbb
+    ports:
+      - "5432:5432"
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+
+volumes:
+  pgdata: