Summary

The cycle lock (held by gbrain dream / autopilot) had no CLI escape hatch, so a wedged cycle stranded it indefinitely and gbrain doctor's hint routed operators to gbrain sync --break-lock which couldn't actually break it.

This PR adds gbrain dream --break-lock with the same safety semantics as the existing gbrain sync --break-lock:

• safe path (no flag): refuses if holder alive, refuses cross-host (process.kill(pid, 0) is invalid across hosts)
• --max-age <seconds>: atomic TOCTOU-safe age-gated DELETE keyed on (id, holder_pid, last_refreshed_at < NOW() - N * INTERVAL)
• --force-break-lock: skip guards, atomic DELETE, loud warning that the holder may still be writing
• --source <id> / --json: per-source scoping (resolves to gbrain-cycle:<id> lock key) and machine-readable output

Doctor at src/commands/doctor.ts:2417+ already routes cycle locks to gbrain dream --break-lock (the if-else chain is in place), so the moment this lands, the existing hint becomes actionable for the first time.

Test plan

• gbrain dream --break-lock (no cycle lock held) → Lock gbrain-cycle is not held (nothing to break). exit 0
• gbrain dream --break-lock while a healthy cycle holds it → holder is alive, use --max-age or --force-break-lock exit 1
• gbrain dream --break-lock --max-age 60 while a long-dead cycle holds it → Broke cycle lock gbrain-cycle ... exit 0
• gbrain dream --break-lock --force-break-lock → atomic DELETE, warning emitted
• gbrain doctor after merge → stale_locks WARN should clear

Files

• src/commands/dream.ts: +129 lines (runCycleLockBreak + formatAgeHuman + --break-lock short-circuit + 3 imports)
• CHANGELOG.md: +4 lines ([Unreleased] section)

Closes #1591