fix: address codex review — use clock for cutoff + early-exit harvest

- cycle.py: use supplied `clock` parameter (not wall time) for the
  lookback cutoff, so deterministic tests/experiments get reproducible
  harvest windows
- harvest.py: break (not continue) when a file is older than since_iso,
  since files are sorted newest-first by mtime — avoids scanning the
  entire transcript directory for quiet projects with large histories

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skillopt_sleep/cycle.py

@@ -150,7 +150,8 @@ def run_sleep_cycle(
             lookback_hours = cfg.get("lookback_hours", 72)
             if lookback_hours and lookback_hours > 0:
                 import time
-                cutoff = time.time() - lookback_hours * 3600
+                ref_time = clock if clock is not None else time.time()
+                cutoff = ref_time - lookback_hours * 3600
                 since = _now_iso(cutoff)
         max_tasks = cfg.get("max_tasks_per_night", 40)
         max_sessions = cfg.get("max_sessions_per_night", 0) or max_tasks * 3