Rebalance swarm: promote all nodes to managers and remove hostname constraints

- Promoted p1, p2, p3 from worker to manager nodes for 4-node quorum
- Removed unnecessary hostname constraints from service configs
- Only traefik and portainer remain pinned to p0
- Services now auto-balance across all nodes via GlusterFS shared storage
- Updated README with cluster overview and distribution strategy

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

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

stacks/apps/n8n/stack.yml

@@ -17,9 +17,6 @@ services:
     - /var/run/docker.sock:/var/run/docker.sock:ro
     deploy:
       replicas: 1
-      placement:
-        constraints:
-        - node.hostname == p0
       restart_policy:
         condition: on-failure
         delay: 5s