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.

server/plugins/migrate.ts

@@ -0,0 +1,13 @@
+import { migrate } from 'drizzle-orm/node-postgres/migrator'
+import { getDb } from '../db/client'
+
+// Apply pending migrations once when the server boots (dev and prod). Skipped
+// when DATABASE_URL is unset (e.g. during build) so it never blocks the bundle.
+export default defineNitroPlugin(async () => {
+  if (!process.env.DATABASE_URL) {
+    console.warn('[migrate] DATABASE_URL not set — skipping migrations')
+    return
+  }
+  await migrate(getDb(), { migrationsFolder: 'server/db/migrations' })
+  console.log('[migrate] migrations applied')
+})