feat(review): inject authoritative scope + diff into reviewer and judge prompts

The parent computes the review scope (commits, files, uncommitted, diff) for its banner, then discards it and tells each child agent only how to re-derive it. That cost minutes of setup per reviewer and let one agent diff a behind-main branch in the wrong direction, reporting mainline evolution as branch regressions — two of four high findings in a real run were such phantoms, and the judge consolidated them unchecked.

ComposeReviewPrompt now renders a parent-computed ScopeContext: commit list (oldest first), three-dot name-status file list, porcelain uncommitted lines, and the diff itself when it fits a 48KiB inline budget (beyond that, the exact three-dot command). The judge prompt gets the authoritative changed-file list with an instruction to discard findings outside it. Lists are capped with truncation flags so agents never mistake a bounded enumeration for an exhaustive one.