Add `genmcp ps` command

[Cali0707]

Depends on #276 #277

Description

Add genmcp ps command to list running servers

Requirements

• Diplay columns: NAME, VERSION, TRANDPORT, PORT, TOOLS, STATUS, STARTED
• Check PID liveness before displaying
• Auto-cleanup dead entries or show with --all flag
• Support --json flag for machine-readable output

Acceptance Criteria

• genmcp ps lists running servers
• Dead processes detected correctly
• --all shows dead entries
• --json outputs valid JSON
• Unit tests
• Documentation updated