[TheGreatAxios]

Closes CL-11529

Why
The portal's code review section showed only reviews from the old standalone code review workflow. Reviews a pull request's manager ran were posted to the pull request but never appeared in the portal.

What changed

• The code review section, and Send to GitHub or Bitbucket, now read the manager's records on both hosts. They show the newest of three things: a review the manager deployed that is still running, the result a review reported, or a review the manager gave up on, such as one past its deadline. Only results one of the manager's passes took, or that come from a review the manager deployed, count. A pull request with none of these shows the same empty state as before.
• A review that did not finish shows only "The last review did not finish", with no reason underneath. The unused failure-reason helper is removed, and the user manual sentence is updated.
• A finished review now reports the hash of the diff it read, so a later commit with the same diff still takes that review over.
• The old standalone reviews are no longer read, so they stop appearing in the portal from this PR until the CL-11525 removal slice deletes the old review feed. The whole stack merges together.
• ARCHITECTURE.md and IMPLEMENTATION.md describe where reviews are read from.

Verified

• Rewrote code-review-runs.postgres.test.ts to cover: no review; a finished review; a failed one; one the manager gave up on; a running one; a result no pass took, which is ignored; the review going to the right host; carrying a review over by its diff hash; and the throttle that stops a failed host read from being retried on every poll. 1 of 1 passes. The old code fails it, because it does not read the manager's records.
• report.test.ts checks that a review reports its diff's hash.
• Hub code review, manager state, server, pr-code-review, triage-manager and triage-contracts tests: 357 of 357 pass.
• bun run check, bun run lint and the policy check pass.

[linear-code]

CL-11529