[Bug] /review high effort silently increased to 10× token cost via multi-agent fan-out

**Bug Description**
Title: /review at high effort silently became ~10× more expensive (single reviewer → 14-agent fan-out) in mid-August '26

Body:

The `/review` skill was aliased to `/code-review`and reimplemented into a multi-agent fan-out at higher effort levels, but the change is invisible at the call site: the same /review at the same high effort now costs roughly an order of magnitude more tokens and wall-clock than days earlier. Effort labels should mean roughly the same work across builds; this one changed under the label with no signal.

- Env: CLI 2.1.237 (Homebrew), model Claude Fable 5, effort high (long-standing default).
- Expected: /review at high costs about what it always did — a single read-only reviewer pass.
- Actual: for a normal +834/-55 PR, one /review high spawned ~14 subagents (~8 code-review finder agent () + ~6 code-review VERIFIER), consumed ~66M tokens (≈59M cache-read), took ~23 min, and was ~20% of a weekly-capped plan for a single review.
- Evidence it's a build change, not usage: the "code-review finder agent ()" / "code-review VERIFIER" prompt signatures appear for the first time on 08-21; before that, reviews used one "stringent code reviewer … READ-ONLY" subagent. Same effort label, ~1 agent → ~14.
- Suggestions: keep effort-label cost stable across builds or surface it (e.g. "this review will fan out to N agents"); consider gating the fleet to xhigh/max or opt-in; document the apparent model-gating (fleet on for Sonnet-5 high+, off for Opus/default) — the model-table vs observed-Fable-fan-out mismatch is confusing.

**Environment Info**
- Platform: darwin
- Terminal: Apple_Terminal
- Version: 2.1.237
- Feedback ID: 3cca2c35-06c0-49ea-931d-1aff32b6ca05

**Errors**
```json
[]
```

Start at the /review alias and /code-review implementation, then inspect the effort-level fan-out and model-table paths mentioned in the report. Reproduce with CLI 2.1.237 at high effort and compare agent count, token usage, and wall-clock against the single-reviewer behavior. Done means cost or agent expansion is stable or clearly surfaced, with model gating documented or corrected.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.