feat: add Coolify deployment platform to dev stack

Add Coolify self-hosted deployment platform with:
- Coolify main service at coolify.dev.pivoine.art
- Dedicated PostgreSQL database (uses shared core instance)
- Soketi WebSocket server for real-time features
- Traefik routing with HTTPS and compression
- Environment variables in arty.yml (secrets in .env)
- Database creation in PostgreSQL init script

Coolify enables deploying applications from Git repositories,
including the pivoine.art Jekyll site from Gitea.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

arty.yml

@@ -155,7 +155,7 @@ envs:
     MEDIA_FILESTASH_IMAGE: machines/filestash:latest
     MEDIA_FILESTASH_TRAEFIK_HOST: filestash.media.pivoine.art
     MEDIA_FILESTASH_CANARY: true
-    # Dev (Gitea + Runner)
+    # Dev (Gitea + Coolify)
     DEV_TRAEFIK_ENABLED: true
     DEV_COMPOSE_PROJECT_NAME: dev
     DEV_GITEA_IMAGE: gitea/gitea:latest
@@ -163,6 +163,9 @@ envs:
     DEV_GITEA_DB_NAME: gitea
     DEV_GITEA_RUNNER_IMAGE: gitea/act_runner:latest
     DEV_GITEA_RUNNER_NAME: docker-runner
+    DEV_COOLIFY_IMAGE: ghcr.io/coollabsio/coolify:latest
+    DEV_COOLIFY_TRAEFIK_HOST: coolify.dev.pivoine.art
+    DEV_COOLIFY_DB_NAME: coolify
     # PairDrop
     DROP_TRAEFIK_ENABLED: true
     DROP_COMPOSE_PROJECT_NAME: drop