v0.4.1 — unattended agent time is not sitting time

Honesty fix: while nobody is touching the machine (macOS keyboard/mouse idle clock, VIBESTRETCH_AWAY, default 5 min), agent activity builds no sitting debt and nudges never fire — an overnight workflow no longer greets you with "33 min sitting" you never sat, and nothing chimes at an empty chair at 3 a.m. Hook payloads without a session_id no longer pool into a shared eternal turn. On Linux the guard degrades to the existing 45-minute reset (documented).