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/install.sh

@@ -9,10 +9,10 @@ AGENTS_SKILLS="${HOME}/.agents/skills"
 
 echo "[install] repo: $REPO_ROOT"
 
-# 1) custom /sleep prompt
+# 1) custom /skillopt-sleep prompt
 mkdir -p "$CODEX_HOME/prompts"
-cp "$REPO_ROOT/plugins/codex/prompts/sleep.md" "$CODEX_HOME/prompts/sleep.md"
-echo "[install] /sleep prompt   -> $CODEX_HOME/prompts/sleep.md"
+cp "$REPO_ROOT/plugins/codex/prompts/skillopt-sleep.md" "$CODEX_HOME/prompts/skillopt-sleep.md"
+echo "[install] /skillopt-sleep prompt   -> $CODEX_HOME/prompts/skillopt-sleep.md"
 
 # 2) user-level skill
 mkdir -p "$AGENTS_SKILLS/skillopt-sleep"
@@ -30,7 +30,7 @@ cat <<EOF
 
   ## SkillOpt-Sleep
   An offline self-improvement cycle is available. To run it:
-  \`bash "$REPO_ROOT/plugins/run-sleep.sh" status\`. Use \`/sleep\` for the guided flow.
+  \`bash "$REPO_ROOT/plugins/run-sleep.sh" status\`. Use \`/skillopt-sleep\` for the guided flow.
 
-Done. Try:  /sleep status
+Done. Try:  /skillopt-sleep status
 EOF