feat(nodes): SSH bootstrap + housekeeping — install script, bundled binaries, auto-prune

- `containr nodes add <user@host>` mints an enroll token, SSHes once,
  runs the install script remotely; --print emits the one-liner
- Public /api/agents/install.sh + /api/agents/download/{platform};
  agent binaries built into the image under /agents
- Agent-side `prune` (bounded docker system prune, volumes opt-in)
  and `system_df` commands
- node_agents.auto_prune + health sweep enqueues daily prune;
  offline/online transitions notify admins
- CLI nodes update/prune/commands + MCP tools (prune confirm-gated)
- Usage page: install one-liner, per-node Prune + auto toggle

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

docs/guides/CLI.md

@@ -72,6 +72,8 @@ import compose <project-id> <compose.yml|->
                                attached under their service name; --var K=V overrides
                                template variables
 nodes list|get|delete|tokens     node agents + onboarding tokens (admin)
+nodes add <user@host>            SSH bootstrap — one session installs the agent, then never needed again (--print for manual runs)
+nodes update|prune|commands      rename/auto-prune, bounded docker prune, command history
 scaling status|policies|services|scale
 ha status|alerts|health|policies|enable|disable|failover
 security scan|vulnerabilities|metrics