feat(status-bar): trace branch PR and CI status

[sudomaggie]

Summary

Adds a branch CI menu to the workstation status bar, sitting between the branch
button and the git sync control. It shows the pull request open for the current
branch and the state of every check on its head commit, grouped failed /
running / skipped / passed, with a link out to each check's details.

The menu reuses the ports menu's trigger and portalled panel so the two
neighbours in the bar read as one control family.

Problem

Tracing a branch's CI meant leaving the app for GitHub, or opening the PR
sidebar panel and switching to its Checks tab. GitHub Desktop surfaces this in
its own status bar; we had the data (github_get_checks, already wired for the
PR detail panel) but no ambient place to read it.

The naive way to add it — a fixed-interval poller — is the wrong trade. Most of
the time a branch's checks have already finished and nothing can change until
the next push, so a periodic timer spends GitHub API budget to re-confirm a
static answer.

Solution

The menu. CiStatusMenu renders only when the branch has an open PR. The
trigger shows a state icon plus #650, and reported/total while checks are
still running. The panel header carries the PR link, the rolled-up status and a
refresh button; rows show the check name, elapsed time only while running, and
a details link. The reporting app (GitHub Actions) is kept out of the label —
it is the same for nearly every row — and appears in the hover title instead.

Bounded polling. useBranchPullRequestStatus gains an opt-in poll mode.
The schedule lives in nextBranchCiPollDelayMs:

Situation	Cadence
Checks running	15s → 30s → 60s, capped at 60s
PR open, no checks reported yet	30s × 3, then stop
Every check has a verdict	no timer
No PR, or checks unreadable	no timer
Window hidden	timer cleared, resumes on return

A new head SHA resets the backoff, so a push is picked up at the fast interval
instead of inheriting a cooled-off one. Opening the menu or hitting refresh
forces a read past the 45s cache TTL. A typical 10-minute CI run costs ~11
reads and then goes quiet; a settled branch costs zero.

The focused-chat rail keeps polling off and shares the same TTL cache and
in-flight coalescing, so mounting both surfaces does not fetch twice.

Shared derivation. Check-state mapping moves to
services/git/ciCheckState.ts, which PrChecksTab now imports instead of
re-deriving it. "Settled" is computed structurally — every run reported —
rather than reading summary.state, because the server-side roll-up
short-circuits to failure while other jobs are still in flight, and the rows
should stay live until they actually finish.

Validation / Test plan

• src/services/git/ciCheckState.test.ts (new) — conclusion mapping across all
  failing/neutral conclusions, run-before-status flattening, app name kept
  unmerged, state counts, and the settle rule including the
  decided-failure-with-a-job-still-running case.
• src/services/git/branchPullRequestStatus.test.ts — poll schedule: stops with
  no PR / unreadable / settled checks, backs off and caps while running, and the
  bounded grace period for a PR with no checks yet.
• src/hooks/git/useBranchPullRequestStatus.test.ts — re-reads while checks run
  and stops once they settle; never schedules a poll when poll is not
  requested. Existing visibility-gating and TTL cases still pass unchanged.
• npx vitest run src/services/git src/hooks/git → 16 files, 81 tests passing.
• tsc --noEmit and eslint clean over the touched files.
• Manual: verified against a real PR — settled state renders with no background
  fetches, opening the menu forces a refresh, details links open externally.

Potential risks

• API budget. Polling adds 3 REST calls per read (find PR → get PR → get
  checks) while checks are running. Bounded as above, well inside the 5000/hr
  authenticated limit, but it is new traffic that did not exist before.
• DROPDOWN_CLASSES.searchContainer. Its class list was extracted into a
  shared PANEL_HEADER_ROW constant that panelHeaderRow also points at. The
  emitted string is identical, so existing consumers are unaffected — but it is
  now a shared definition, and changing it moves both.
• PrChecksTab refactor. It now imports checkRunState /
  statusContextState rather than defining them. Behaviour is unchanged; the
  sidebar still shows the app-qualified check name, only the status-bar menu
  drops the prefix.
• i18n coverage. New workstation.ci.* keys were added to en and zh
  only, matching the recent two-locale convention. Other locales fall back to
  English until translated.