The watchdog used to time.sleep(timeout) then immediately SIGKILL, which cut
claude off mid-write and left half-written artifacts. It now sends SIGTERM,
polls os.kill(pid, 0) for up to agent_kill_grace_seconds, and only SIGKILL if
the process is still alive; ProcessLookupError is tolerated at every step.
Timeout is now configurable via config.py: agent_timeout_seconds (default 1800),
agent_kill_grace_seconds (default 20), and agent_timeout_overrides_json for
per-agent overrides (e.g. {"reviewer": 3600}). AGENT_TIMEOUT is kept as a
backward-compatible alias. The recorded exit_code stays -9 so the ORCH-1
monitor retry/fail logic is unchanged (timeout-kills classify as permanent and
requeue within max_attempts, no retry loop).
_auto_merge_pr had zero callers (merge is handled by the deployer agent).
Removed the method; _ensure_pr (still used by the auto-advance path) is kept.
