Add bounded JSON Lines output for logs and follow mode

[delaudio]

Parent epic: #31

Problem

Editor integrations need a cancellable log stream with service and stream identity. Plain terminal lines are ambiguous when multiple services are followed.

Scope

Add an opt-in JSON Lines format:

hum <project> <template> logs [service] --format jsonl --lines 200
hum <project> <template> logs [service] --format jsonl --follow

Each line should be one independently parseable event.

Acceptance criteria

• Every event includes schemaVersion, service name, stream identity, and message text.
• Events include a timestamp or an explicit null when the source has none.
• Snapshot and follow modes use the same event schema.
• Multi-service follow output can be attributed without parsing message prefixes.
• Existing redaction, line-size, retention, and memory bounds still apply.
• Consumer cancellation terminates followers and child processes cleanly.
• Rotation and snapshot-to-follow transitions do not duplicate or drop completed lines.
• Structured errors do not appear as malformed JSONL events.
• Existing plain log output remains the default.