feat(sleep): SkillOpt-Sleep plugin update (preview) — engine robustness + scheduling

Updates the SkillOpt-Sleep plugin on top of the current main. User-facing and
engine improvements since the initial drop:

* Command renamed /sleep -> /skillopt-sleep across Claude Code + Codex shells;
  refreshed plugin READMEs and install scripts.
* Built-in scheduling (skillopt_sleep/scheduler.py + __main__): schedule /
  unschedule the nightly cycle without external cron wiring.
* Backend robustness: bounded retry with backoff (no more silent empty-string
  on transient 429/timeout), content-filter-safe rollout prompt, an
  output-contract guardrail that rejects edits violating the task's required
  format, and a per-sample cache key so repeated dream rollouts are independent
  samples (fixes degenerate single-sample reflection).
* consolidate / rollout / replay: parallel multi-rollout dreaming, gate-mode
  controls, TaskRecord.system framing field.

Scope: this commit ships only the plugin engine + shells. Research/benchmark
harnesses and their data are intentionally not included; the public package
has no dependency on them (the one research-evaluator import is now guarded).
Marked as an early preview in the README; we'll keep iterating.

99/99 unit tests pass.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

plugins/claude-code/scripts/install-cron.sh

@@ -17,7 +17,7 @@ cat <<EOF
 # ── SkillOpt-Sleep nightly cycle ────────────────────────────────────────────
 # Review past sessions, replay tasks, stage validated memory/skill updates.
 # Runs at ${HOUR}:$(printf '%02d' $MIN) local every day. Output goes to the project's
-# .skillopt-sleep/ dir; nothing live is changed until you run '/sleep adopt'
+# .skillopt-sleep/ dir; nothing live is changed until you run '/skillopt-sleep adopt'
 # (unless you pass --auto-adopt below).
 #
 # Copy the next line into 'crontab -e':