Add docker-compose for local Postgres and fix the setup docs

Adds docker-compose.yml (Postgres on host port 5433, to avoid clashing
with another project's container already using 5432 on this machine)
and .env.example so `docker compose up -d` + `cp .env.example .env.local`
gets a working local DB. Adds a db:seed script alongside the existing
db:* scripts.

Rewrites README's "Adding a Database" section, which still described
Better Auth's DB as optional/hypothetical even though this project
already requires Postgres for both its own data and Better Auth's
tables. Fills in CLAUDE.md's Data layer connection-details placeholder
and fixes two more stale pnpm references and a wrong migrations path
(src/db/migrations/ instead of the actual drizzle/) found nearby.

Also fixes a real bug the new docs surfaced: `npm run db:seed` didn't
load .env.local the way drizzle-kit does, so DATABASE_URL was silently
unset when run as documented. seed.ts now loads env the same way
drizzle.config.ts already does.

Verified the full documented flow end-to-end against a fresh container:
migrate, better-auth migrate, seed, dev server, real page render.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -9,6 +9,10 @@ npm install
 npm run dev
 ```
 
+This requires a running Postgres database — see
+[Local development database](#local-development-database) below before your
+first run.
+
 # Building For Production
 
 To build this application for production:
@@ -42,39 +46,44 @@ npm run check
 ```
 
 
-## Setting up Better Auth
+## Local development database
 
-1. Generate and set the `BETTER_AUTH_SECRET` environment variable in your `.env.local`:
-
-   ```bash
-   npx -y @better-auth/cli secret
-   ```
-
-2. Visit the [Better Auth documentation](https://www.better-auth.com) to unlock the full potential of authentication in your app.
-
-### Adding a Database (Optional)
-
-Better Auth can work in stateless mode, but to persist user data, add a database:
-
-```typescript
-// src/lib/auth.ts
-import { betterAuth } from "better-auth";
-import { Pool } from "pg";
-
-export const auth = betterAuth({
-  database: new Pool({
-    connectionString: process.env.DATABASE_URL,
-  }),
-  // ... rest of config
-});
-```
-
-Then run migrations:
+This project requires a Postgres database — both for its own data (Drizzle,
+see `src/db/schema.ts`) and for Better Auth's own tables (users, sessions,
+etc). A `docker-compose.yml` at the repo root starts one:
 
 ```bash
-npx -y @better-auth/cli migrate
+docker compose up -d           # starts Postgres on localhost:5433
+cp .env.example .env.local     # sets DATABASE_URL to match
+npm run db:migrate             # applies this project's Drizzle migrations
+npx @better-auth/cli migrate   # applies Better Auth's own tables
+npm run db:seed                # seeds a sample Brand, menu, and Machines
+npm run dev
 ```
 
+`DATABASE_URL` in `.env.local` is picked up automatically by both the dev
+server and the `drizzle-kit` commands above — no other wiring needed.
+
+After changing `src/db/schema.ts`, generate and apply a new migration rather
+than editing the database by hand:
+
+```bash
+npm run db:generate
+npm run db:migrate
+```
+
+## Setting up Better Auth
+
+Generate and set the `BETTER_AUTH_SECRET` environment variable in your
+`.env.local`:
+
+```bash
+npx -y @better-auth/cli secret
+```
+
+See the [Better Auth documentation](https://www.better-auth.com) for more on
+configuring authentication.
+
 
 
 ## Routing