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.

Dockerfile

@@ -4,9 +4,8 @@
 FROM node:24-alpine AS build
 RUN corepack enable
 WORKDIR /app
-COPY package.json pnpm-lock.yaml ./
-RUN pnpm install --frozen-lockfile
 COPY . .
+RUN pnpm install --frozen-lockfile
 RUN pnpm build
 
 # --- Runtime stage: minimal image running the built server ---