feat(sleep): real claude + codex backends, gbrain-evals benchmark, rule judges

Upgrade from mock-only to REAL multi-backend validation:

Backends (skillopt/sleep/backend.py):
  - CliBackend base: shared attempt/judge/reflect prompts, response cache,
    token accounting. Subclasses implement only _call().
  - ClaudeCliBackend: drives `claude -p --output-format text`.
  - CodexCliBackend: drives the REAL @openai/codex `exec -o <file>` for clean
    output; resolve_codex_path() skips the hermes wrapper at ~/.local/bin/codex.
  - reflect() now aggregates the exact failing judge criteria into the prompt
    (gbrain's lesson: tell the optimizer what the scorer rewards).

Rule judges (skillopt/sleep/judges.py): gbrain-compatible local scorers
  (section_present / regex / max_chars / contains / tool_called) — held-out
  scoring with no judge-API spend. TaskRecord gains a `judge` field +
  reference_kind="rule".

gbrain-evals adapter (experiments/gbrain_bench.py, run_gbrain.py): load
  garrytan/gbrain-evals skillopt-v1 deficient skills + train/held-out task
  sets and run our consolidate() loop against the SAME suite gbrain scores.

REAL results (docs/sleep/real_api_results.md), brief-writer seed, 1 night:
  - Claude (Haiku): held-out 0.00 -> 1.00
  - Codex:          held-out 0.00 -> 0.67
  Both proposed a correct, general format rule into the protected LEARNED block.

CLI: --backend {mock,claude,codex}, --codex-path, --model; experiment +
gbrain runners gain --limit-* cost controls. 17 tests pass.

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

skillopt/sleep/__main__.py

@@ -34,8 +34,9 @@ from skillopt.sleep.staging import latest_staging, adopt as adopt_staging
 def _add_common(p: argparse.ArgumentParser) -> None:
     p.add_argument("--project", default="")
     p.add_argument("--scope", default="", choices=["", "all", "invoked"])
-    p.add_argument("--backend", default="", choices=["", "mock", "anthropic"])
+    p.add_argument("--backend", default="", choices=["", "mock", "claude", "codex"])
     p.add_argument("--model", default="")
+    p.add_argument("--codex-path", default="", help="path to the real @openai/codex binary")
     p.add_argument("--claude-home", default="", help="override ~/.claude (also isolates state)")
     p.add_argument("--lookback-hours", type=int, default=0)
     p.add_argument("--edit-budget", type=int, default=0)
@@ -54,6 +55,8 @@ def _cfg_from_args(args) -> Any:
         overrides["backend"] = args.backend
     if args.model:
         overrides["model"] = args.model
+    if getattr(args, "codex_path", ""):
+        overrides["codex_path"] = os.path.abspath(args.codex_path)
     if getattr(args, "claude_home", ""):
         overrides["claude_home"] = os.path.abspath(args.claude_home)
     if getattr(args, "lookback_hours", 0):