feat(portainer): add Portainer-optimized deployment files

- Create docker-compose.portainer.yml
  - No env_file directive (Portainer doesn't support it)
  - Port exposed on 0.0.0.0 (Portainer limitation)
  - Simple depends_on syntax
  - All environment variables explicit

- Create docs/PORTAINER-DEPLOYMENT.md
  - Complete Portainer deployment guide
  - Step-by-step instructions
  - Environment variables reference
  - Troubleshooting section
  - Best practices for security and backups

- Update README.md
  - Add Portainer deployment section
  - Reference Portainer deployment guide

Fixes:
- 'open /data/compose/94/.env: no such file or directory'
- 'ignoring IP-address (127.0.0.1:8200:8200/tcp)' warning

Portainer requires different compose syntax than standard docker-compose.
This provides a deployment path optimized for Portainer's stack parser.

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

README.md

@@ -208,6 +208,29 @@ docker stack ps mosaic
 
 See [Docker Swarm Deployment Guide](docs/SWARM-DEPLOYMENT.md) and [Quick Reference](docs/SWARM-QUICKREF.md) for complete documentation.
 
+### Portainer Deployment
+
+**Recommended for GUI-based stack management.**
+
+Portainer provides a web UI for managing Docker containers and stacks. Use the Portainer-optimized compose file:
+
+**File:** `docker-compose.portainer.yml`
+
+**Key differences from standard compose:**
+
+- No `env_file` directive (define variables in Portainer UI)
+- Port exposed on all interfaces (Portainer limitation)
+- Optimized for Portainer's stack parser
+
+**Quick Steps:**
+
+1. Create `mosaic_internal` overlay network in Portainer
+2. Deploy `mosaic-openbao` stack with `docker-compose.portainer.yml`
+3. Deploy `mosaic` swarm stack with `docker-compose.swarm.yml`
+4. Configure environment variables in Portainer UI
+
+See [Portainer Deployment Guide](docs/PORTAINER-DEPLOYMENT.md) for detailed instructions.
+
 ## Project Structure
 
 ```