CLI "doctor" command for storage + mesh health

[kayodebristol]

Context

Production users need a quick health check for storage, WAL, and mesh connectivity. A CLI doctor/status command will improve supportability and debugging.

Tasks

• Add pluresdb doctor (or status) command
• Report storage engine status, WAL replay health, and disk usage
• Report sync transport status (mode, peers, last activity)
• Emit JSON output option for automation

Acceptance Criteria

• Command runs without side effects and exits non-zero on failures
• Output includes actionable remediation hints
• JSON output is machine-readable and stable