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.

docs/adr/0003-use-coolify-managed-postgres-over-sqlite.md

@@ -18,5 +18,6 @@ switch to **Coolify-managed PostgreSQL** (via Drizzle's `pg` driver).
   prod — one more moving part than a single file.
 - **Supersedes** the SQLite choice in DESIGN.md (T5, F10) and the original
   `/deep-design` decision.
-- Unchanged: deploys must **not** auto-run from `main` (every merge would deploy);
-  use a tagged release or manual trigger.
+- Autodeploy from `main` is enabled (Coolify watches the repo and deploys on
+  push); `main` must be protected with required PR review + CI so only vetted
+  commits reach production.