DevOps: Coolify-Testserver-Deployment (Compose, Migrations-Job, Runbook)

- docker-compose.coolify.yml: Coolify-taugliche Variante (kein host-port,
  Env via Coolify-Variablen, migrate-Init-Job vor app, app-Healthcheck)
- .env.coolify.example: Referenz der Coolify-Env-Variablen (nur Platzhalter)
- docs/DEPLOY-COOLIFY.md: Runbook (Gitea-Deploy-Key, Ressource, Env, Domain, Seed)
- .gitignore: .env.coolify.example whitelisten

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -33,6 +33,7 @@ yarn-error.log*
 # env files (can opt-in for committing if needed)
 .env*
 !.env.example
+!.env.coolify.example
 
 # vercel
 .vercel