Bastion tunnel reuse via azlin --port

[rysweet]

Each azlin connect creates a new Bastion tunnel. Check if azlin supports --port to reuse existing tunnels from azlin list (ports 50000-50004). If so, add a _get_cached_tunnel_port() helper.

Files to modify:

• src/amplihack/fleet/fleet_tui.py
• src/amplihack/fleet/_session_gather.py
• src/amplihack/fleet/fleet_session_reasoner.py

Requirements:

1. First check azlin --help to see if --port flag exists
2. Parse azlin list output to find active tunnel ports
3. Add _get_cached_tunnel_port(vm_name) helper that returns existing port or None
4. When port exists, use ssh localhost -p PORT instead of azlin connect
5. Fall back to azlin connect when no cached tunnel
6. All 918+ fleet tests must pass
7. Commit changes on this branch

[rysweet]

Fixed by PR #2937 (merged).