docs: add visible slice local workflow

Document the migration/seed/API/web workflow in a root README, add an
API e2e smoke test that always checks /api/health and additionally
exercises the real DatabaseModule/seeded data plus the arrivesAt
validation rejection when DATABASE_URL is available, and add a
`test:e2e` root script.

Also fix `.env` loading so the documented root-level `.env` is actually
found: `main.ts` never loaded dotenv at all, and `data-source.ts`
loaded it relative to `process.cwd()`, which is `apps/api` (not the
repo root) whenever npm runs a `--workspace` script. Both now resolve
the repo-root `.env` explicitly. Also narrowed the CLI migrations glob
to numeric-prefixed files so it no longer tries to load the colocated
`*.migration.spec.ts` as a migration.

Verified end-to-end against a real PostgreSQL instance: migrate, seed
twice (idempotent), start the API, and exercise every documented route
including a rejected POST /api/travel body containing arrivesAt.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

apps/api/src/database/data-source.ts

@@ -1,6 +1,14 @@
-import 'dotenv/config';
+import { config } from 'dotenv';
+import { resolve } from 'path';
 import { DataSource } from 'typeorm';
 
+// npm workspace scripts (`db:migrate`, `db:seed`) run with this file's
+// workspace (`apps/api`) as the current working directory, not the repo
+// root where the documented `.env` lives. Resolve it explicitly so the
+// documented `npm run db:migrate` / `npm run db:seed` flow works regardless
+// of the caller's working directory.
+config({ path: resolve(__dirname, '../../../../.env') });
+
 const databaseUrl = process.env.DATABASE_URL;
 
 if (!databaseUrl?.trim()) {
@@ -11,6 +19,6 @@ export const AppDataSource = new DataSource({
   type: 'postgres',
   url: databaseUrl,
   entities: [__dirname + '/../**/*.entity.{ts,js}'],
-  migrations: [__dirname + '/migrations/*.{ts,js}'],
+  migrations: [__dirname + '/migrations/[0-9]*.{ts,js}'],
   synchronize: false,
 });