refactor(ci): review pull requests with one senior-engineer role

The review job ran the official code-review plugin, which fans a pull
request out to five Sonnet reviewers plus a Haiku scorer per finding and
drops everything scored under 80, and the briefing file spent most of its
lines overriding that plugin. Both are gone: the job hands one Senior
Software Engineer prompt to the action inline, the way the issue analyst
does, and denies the Agent tool so the single role is mechanical rather
than a request.

REVIEW.md moves from the emoji markers to CRITICAL/HIGH/MEDIUM/LOW with a
pre-existing qualifier. The uncapped rule is scoped to findings the pull
request introduced or worsened so it cannot collide with the cap of three
pre-existing ones. "A finding is a report, not a patch" stays as it was.

Workflow housekeeping: GH_TOKEN, REPO and PR live in the job env instead
of six step copies; the skip gate is per pull request, so a head pushed
after the automatic review is reviewed only on @claude review; the comment
counters sum gh's per-page jq output, which read "0\n0" as a review on a
pull request with more than 100 comments; --max-turns rises to 300 because
every read now costs the single agent a turn instead of a subagent.

.github/claude/repo-context.md

@@ -3,9 +3,8 @@
 Briefing for the issue analyst in `.github/workflows/claude-issue-analyst.yml`.
 It exists so these facts live in ONE place next to the code instead of being
 restated in the prompt, where they went stale silently. (Pull-request review is
-separate: the code-review skill in `.github/workflows/claude-pr-review.yml` is
-briefed with `CLAUDE.md`, `REVIEW.md` and `.github/claude/review-job.md`, not
-this.)
+separate: the reviewer in `.github/workflows/claude-pr-review.yml` is briefed by
+its own prompt, `CLAUDE.md` and `REVIEW.md`, not this.)
 
 `CLAUDE.md`, `frontend/CLAUDE.md` and `docs/architecture.md` outrank this file.
 Where they disagree with it, they win and this file is the thing to fix.

.github/claude/review-job.md

@@ -1,81 +0,0 @@
-# Review job briefing
-
-Appended to the system prompt of the pull-request review job in
-`.github/workflows/claude-pr-review.yml`. The workflow adds a "This run" section
-after it, naming the repository, the pull request, the pinned head SHA, the
-trigger and the command that reads CI's verdict. `REVIEW.md` at the repository
-root is the review rubric; this file only says how that rubric is applied in a
-headless CI run, and where the code-review skill's own habits give way to it.
-
-## Read REVIEW.md first
-
-Before reviewing, read `REVIEW.md` and follow it: the severity marker every
-finding carries, what counts as Important in this repository, what not to
-report, the repo-specific checks, the verification bar and the volume cap. The
-skill loads `CLAUDE.md` on its own; it does not load `REVIEW.md`, which is why
-this briefing exists.
-
-Where the skill and `REVIEW.md` disagree, `REVIEW.md` wins. The skill treats
-a pre-existing issue as a false positive, and a real issue on a line the pull
-request did not modify too; here severity follows what the change caused, not
-which lines it touched — a defect it introduced a frame outside the diff is
-🔴 when it lands in an Important class, one it did not cause is 🟣, up to
-three of those get posted, and a live security hole on an exposed surface
-opens the summary.
-
-It also filters out every issue its confidence pass scores under 80 and posts
-nothing once that empties the list; that rubric scores a nitpick 50,
-`REVIEW.md` allots five nits, and the comment goes up either way. It says to
-avoid emojis, and the whole severity system is three of them. Its "Found N
-issues" format gives way to the tally, findings and coverage list below, and
-its rule against reading build signal gives way to "CI is the build".
-
-## A finding is a report, not a patch
-
-Never post a `suggestion` block, and never write the fix: no patch, no
-replacement snippet, no rewritten function, no "suggested fix" section, in the
-summary and in an inline comment alike. The prompt that launches this job
-passes `--comment` after the command; the skill defines no such flag, and it
-is not a licence to attach a suggestion to a small fix. How narrow the one
-clause naming where the fix belongs has to be, and what a finding says
-instead, is `REVIEW.md`'s "A finding is a report, not a patch" — read it
-there rather than from memory. The maintainer decides the change.
-
-## Skip gate
-
-An existing review comment justifies skipping only when its `Reviewed head:`
-line names the head SHA of this run. When the head has moved on, or this run
-was triggered by an `@claude review` comment, review in full, focusing on the
-commits since the previously reviewed head, and apply the rounds rule in
-`REVIEW.md`: after the first review of a pull request, 🔴 findings only.
-
-## Headless run
-
-This run ends the moment you end your turn. Launch every subagent with
-`run_in_background` set to false and wait for its result inside the same turn.
-Never end the turn while a subagent is still running, and never before the
-review comment is posted: a run that ends without posting has failed.
-
-## What is checked out where
-
-The working tree is the BASE branch. A read-only checkout of the pull request
-head sits beside it in `pr-head/`: read and grep the changed files there, and
-treat anything read outside it as the pre-merge baseline, not as the code
-under review. Never build, install or execute anything from `pr-head/`. This
-job holds a write-scoped token, so running pull-request code with it is the
-workflow vulnerability `REVIEW.md` calls blocking.
-
-## CI is the build
-
-You cannot build or test here, but CI already ran on the head SHA. Read its
-check runs with the command under "This run" and report what they concluded
-instead of writing that verification was unavailable. A required check that
-failed, or that never ran on this head, is itself a finding.
-
-## The comment
-
-The comment you post is the only part of this run anyone sees. It opens with
-the tally, carries a `Reviewed head:` line naming the head SHA under "This
-run", and ends with the coverage list `REVIEW.md` asks for, whether or not you
-found anything. Inline comments anchor findings to lines; the summary comment
-carries the tally, the head and the coverage.