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/codex/README.md

@@ -23,7 +23,7 @@ three, plus a shared runner.
 ```bash
 git clone <repo-url> SkillOpt-Sleep
 cd SkillOpt-Sleep
-bash plugins/codex/install.sh          # installs the /sleep prompt + skill
+bash plugins/codex/install.sh          # installs the /skillopt-sleep prompt + skill
 export SKILLOPT_SLEEP_REPO="$(pwd)"    # so the runner is found from anywhere
 ```
 
@@ -32,10 +32,10 @@ Requires Python ≥ 3.10 and the `codex` CLI on PATH.
 ## Use
 
 ```text
-/sleep status      # what's happened
-/sleep dry-run     # safe preview, stages nothing
-/sleep run         # full cycle, stages a reviewed proposal (no live edits)
-/sleep adopt       # apply the staged proposal (with backup)
+/skillopt-sleep status      # what's happened
+/skillopt-sleep dry-run     # safe preview, stages nothing
+/skillopt-sleep run         # full cycle, stages a reviewed proposal (no live edits)
+/skillopt-sleep adopt       # apply the staged proposal (with backup)
 ```
 
 Or call the engine directly: