docs: rewrite new-dev setup guide (env, seed, tests, gotchas) (#529)

Rewrites docs/GETTING_STARTED.md as the canonical "how to run this
project" guide and fixes the README quick start.

Corrections to what was there:
- README told devs to open localhost:3000 — tenant resolution reads the
  subdomain, so localhost bounces every authenticated page to
  /join-school. Both docs now say lvh.me:3000 and explain why.
- Guide recommended cloud Supabase first and `db push` for local setup;
  local flow is `supabase start` + `npm run db:reset`.
- Guide said to confirm signup email via Mailpit — email confirmations
  are disabled locally (config.toml enable_confirmations = false).

Adds what new devs were missing:
- Copy-paste .env.local block with the local Supabase keys.
- Seed-account table annotated with which subdomain to log in on.
- Full seed inventory (tenants free vs enterprise and why, courses,
  products, plans, alice's pre-seeded subscription) and why the seed
  hand-writes auth.users — handle_new_user() doesn't fire on SQL insert.
- Migration workflow, unit + E2E test rules (dev server first, lvh.me,
  workers=1), Stripe CLI's two distinct webhook secrets, cron secret,
  mcp-server's port-3000 clash with next dev.
- Troubleshooting: join-school bounce, port clash + the
  site_url=localhost:3005 in config.toml, stale JWT after role change,
  the tables with no tenant_id that error the whole query.


Claude-Session: https://claude.ai/code/session_01853LDokPbhv9Kg9Ctz9DB5

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: guillermoscript

README.md

@@ -23,22 +23,45 @@ A multi-tenant SaaS Learning Management System. Schools run on subdomains (`scho
 2. **Configure environment**
    ```bash
    cp .env.example .env.local
-   # Fill in at minimum: NEXT_PUBLIC_SUPABASE_URL, NEXT_PUBLIC_SUPABASE_PUBLISHABLE_OR_ANON_KEY, SUPABASE_SERVICE_ROLE_KEY
+   ```
+   For local Supabase, set these four. Run `supabase status` (after step 3) and copy its **Publishable** and **Secret** keys — they are local-only dev keys, the same on every machine:
+   ```bash
+   NEXT_PUBLIC_SUPABASE_URL=http://127.0.0.1:54321
+   NEXT_PUBLIC_SUPABASE_PUBLISHABLE_OR_ANON_KEY=<Publishable key from `supabase status`>
+   SUPABASE_SERVICE_ROLE_KEY=<Secret key from `supabase status`>
+   NEXT_PUBLIC_PLATFORM_DOMAIN=lvh.me:3000
    ```
 
 3. **Start local Supabase** _(requires Docker)_
    ```bash
    supabase start
-   supabase db reset   # applies all migrations + seeds test data
+   npm run db:reset   # applies all migrations + seeds tenants, users, courses, products
    ```
 
 4. **Run the dev server**
    ```bash
    npm run dev
    ```
 
-5. **Open the app**
-   Visit `http://localhost:3000` — or use a tenant subdomain like `http://testschool.lvh.me:3000`
+5. **Open the app at `http://lvh.me:3000` — not `localhost`**
+
+   Tenant resolution reads the subdomain; `lvh.me` resolves `*.lvh.me` to `127.0.0.1`. On `localhost` no tenant resolves and authenticated pages bounce to `/join-school`.
+
+   - `http://lvh.me:3000` — Default School (free plan)
+   - `http://code-academy.lvh.me:3000` — Code Academy Pro (enterprise plan)
+
+6. **Log in** with a seeded account (all passwords `password123`), on the subdomain matching its tenant:
+
+   | Email | Tenant | Role |
+   |--|--|--|
+   | `student@e2etest.com` | Default School (`lvh.me:3000`) | student |
+   | `owner@e2etest.com` | Default School (`lvh.me:3000`) | admin + super admin |
+   | `creator@codeacademy.com` | Code Academy (`code-academy.lvh.me:3000`) | admin |
+   | `alice@student.com` | Code Academy (`code-academy.lvh.me:3000`) | student |
+
+   Local-dev credentials only — seeded by `npm run db:reset`.
+
+**Full walkthrough — seed contents, migrations, tests, optional services, troubleshooting: [`docs/GETTING_STARTED.md`](docs/GETTING_STARTED.md).**
 
 ## npm Scripts
 
@@ -47,14 +70,17 @@ A multi-tenant SaaS Learning Management System. Schools run on subdomains (`scho
 | `npm run dev` | Start dev server |
 | `npm run build` | Production build (TypeScript + lint) |
 | `npm run lint` | Run ESLint |
-| `npm test` | Run Playwright E2E tests |
+| `npm run typecheck` | `tsc --noEmit` |
+| `npm run test:unit` | Vitest unit tests |
+| `npm test` | Playwright E2E tests (dev server must already be running) |
 | `npm run db:reset` | Reset local DB (migrations + seed) |
 | `npm run db:push` | Push migrations to cloud Supabase |
+| `npm run db:types` | Regenerate `lib/database.types.ts` |
 | `npm run mcp:build` | Build the MCP server sub-project |
 
 ## Documentation
 
-- [`docs/GETTING_STARTED.md`](docs/GETTING_STARTED.md) — full local setup guide
+- [`docs/GETTING_STARTED.md`](docs/GETTING_STARTED.md) — **full local setup guide: env, seed data, migrations, tests, troubleshooting**
 - [`CLAUDE.md`](CLAUDE.md) — architecture reference for AI agents and developers
 - [`docs/DATABASE_SCHEMA.md`](docs/DATABASE_SCHEMA.md) — complete DB schema
 - [`docs/AUTH.md`](docs/AUTH.md) — authentication flows