ci: Coolify autodeploy from main; migrate-on-boot and split dev/prod compose

- Add Nitro plugin to apply Drizzle migrations on server boot (skips when
  DATABASE_URL is unset, e.g. during build).
- Split compose: docker-compose.dev.yml (hot-reload + Postgres) vs
  docker-compose.yml (production/self-host, env-driven, Coolify-deployable).
- Add .dockerignore; parameterise compose env; document the autodeploy
  decision (Coolify watches main, no CI workflow needed) in ADR 0003 and
  plan.md T12.

.env.example

@@ -4,6 +4,11 @@ NUXT_SESSION_SECRET=change-me
 # Database (Postgres) — Coolify-managed in prod, docker-compose in dev
 DATABASE_URL=postgres://andon:andon@localhost:5432/andon
 
+# Credentials for the bundled Postgres service in docker-compose.yml
+POSTGRES_USER=andon
+POSTGRES_PASSWORD=andon
+POSTGRES_DB=andon
+
 # Google OAuth (Task 9) — restricted to the theodo.com hosted domain
 GOOGLE_CLIENT_ID=
 GOOGLE_CLIENT_SECRET=