tool-build: build MyReviewer (flag correctness bugs on a PR)

[lorenzoliuzzo]

Part of the fleet milestone (#1 §2). Design: mythings-core/docs/tools/my-reviewer.md.

MyReviewer flags correctness bugs on an open PR (a fleet-native /code-review).

Blocked by

• mythings-core#35 — needs GitHub.diff(number) to read the PR under review.

Scope (v0)

• Input: an open PR number.
• Pre-work: fetch the diff (via Wire mydashboard render into the fleet cycle #35), optionally narrow with MySearcher's ranking.
• One Engine call: identify likely correctness bugs.
• Output: review comments; never merges.

Steps

• Land Wire mydashboard render into the fleet cycle #35 first.
• Scaffold + implement + tests (mock the diff boundary).