AllNighter 1.2.0 — agent-hold leases

Agent holds are now leases, not latches.

• A hold not refreshed for leaseSeconds (default 30 minutes) expires on its own, so an agent session that crashes or is killed without releasing can no longer keep the Mac awake indefinitely.
• Re-POSTing /agent/on?id=X with the same id refreshes the lease — the agent-awake hooks (v1.1.0+) do this automatically on every tool call.
• GET /agent/status now reports ageSeconds (per held id, seconds since last refresh) and leaseSeconds.
• ALLNIGHTER_AGENT_LEASE_SECONDS env override (min 5) for testing.
• User switches are untouched: leases apply only to the agent switch, and agent-off still never overrides user-on.

Notarized universal build, stapled: AllNighter-1.2.0.zip.