Add JSON output for service status

[delaudio]

Parent epic: #31

Problem

Status is currently rendered as a human-oriented table, which is not a stable API for editor integrations.

Scope

Add an opt-in structured mode:

hum <project> <template> status --json

Each service record should expose safe structured state already modeled by Hum, including process, port, health, presentation state, identifiers, timestamps, and diagnostic detail where available.

Acceptance criteria

• status --json uses the common versioned envelope.
• Every selected service has a stable name and explicit process, port, health, and presentation states.
• Optional fields are represented consistently as null or omitted according to the documented schema.
• No environment values or secret material are serialized.
• Ordering is deterministic.
• Stale and missing runtime entries are represented without losing diagnostics.
• Exit behavior for degraded services is documented and fixture-tested.
• Existing table output remains unchanged when --json is absent.