Repo-aware review of an implementation PR (the `ai:done` PR) against the SPEC it implements, the constitution, the ADRs, and the doc-staleness rules. Use when a routine fires on a PR labelled `ai:done`, when a human says "review impl PR #NNN" / "review the implementation for SPEC-NNN", or as a self-review step inside `implement-spec` before the PR is opened. Read-only — produces a structured report and never edits code or merges.