fix(swarm): move docker-compose.swarm.yml back to root directory

- Move docker/docker-compose.swarm.yml to root
- Update documentation references
- Simplifies deployment: swarm file in root, standalone file in root
- Deploy script already expects file in root

Rationale: Keep it simple - two compose files for two deployment methods:
  - docker-compose.yml → standalone (docker compose up -d)
  - docker-compose.swarm.yml → swarm (docker stack deploy)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -201,7 +201,7 @@ docker stack ps mosaic
 **Important Notes:**
 
 - Swarm does NOT support docker-compose profiles
-- To use external services (PostgreSQL, Authentik, etc.), manually comment them out in `docker/docker-compose.swarm.yml`
+- To use external services (PostgreSQL, Authentik, etc.), manually comment them out in `docker-compose.swarm.yml`
 - OpenBao requires manual initialization (no auto-init sidecar in swarm mode)
 
 See [Docker Swarm Deployment Guide](docs/SWARM-DEPLOYMENT.md) and [Quick Reference](docs/SWARM-QUICKREF.md) for complete documentation.