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>

skillopt_sleep/types.py

@@ -54,6 +54,12 @@ class TaskRecord:
     project: str
     intent: str                       # what the user wanted (the "question")
     context_excerpt: str = ""         # minimal context needed to attempt it
+    # Optional system framing for the rollout. When set (e.g. real benchmarks
+    # carrying the research repo's exact rollout_system), the backend uses THIS
+    # verbatim instead of its generic instruction wrapper — this keeps scoring
+    # faithful to the source task and avoids re-deriving framing the benchmark
+    # already bakes in.
+    system: str = ""
     attempted_solution: str = ""      # what the agent produced before
     outcome: str = "unknown"          # success | fail | mixed | unknown
     reference_kind: str = "none"      # exact | rubric | rule | none