fix: address codex round 2 — revert harvest break + allow lookback 0

- harvest.py: revert break to continue — mtime ordering can diverge
  from embedded ended_at timestamps (copy/touch), so we must check all
  files rather than early-exiting on the first old one
- cycle.py: use `is not None and > 0` so lookback_hours=0 means
  "scan full history" (opt-out of the cutoff)
- __main__.py: propagate --lookback-hours 0 to config as explicit 0

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

skillopt_sleep/harvest.py

@@ -294,9 +294,10 @@ def harvest(
         if not _project_matches(d.project or "", scope, invoked_project):
             continue
         if since_iso and d.ended_at and d.ended_at < since_iso:
-            # Files are sorted newest-first by mtime; once we see one that
-            # is older than the cutoff, all remaining files are older too.
-            break
+            # Note: files are sorted by mtime but we compare the embedded
+            # ended_at timestamp — mtime can diverge (copy/touch), so we
+            # cannot break here; we must continue to check all files.
+            continue
         digests.append(d)
         if limit and len(digests) >= limit:
             break