SSH reverse tunnel should use dynamic port allocation #1

Problem

The SSH reverse tunnel in ssh-manager.ts hardcodes port 3000 on the remote side and 3010 on the local side:

await this.setupReverseTunnel(config.id, 3000, 3010);

This has two issues:

1. The local port should use WEB_PORT (now configurable via ATOO_PORT env var) instead of hardcoded 3010
2. The remote port (3000) might already be in use on the remote machine — it should be dynamically allocated

Suggested approach

1. Request port 0 on the remote side so SSH picks a free port
2. Pass the allocated port as ATOO_PORT env var when spawning the agent on the remote machine, so the MCP server connects to the correct tunneled port

Context

Remote agent spawning over SSH is not fully wired up yet — the reverse tunnel is prep work. This should be addressed when implementing SSH remote agents.