test(ui): refresh two stale baselines and settle whether they gate

`make ui-visual` had been red on main since #27, and nothing runs it,
so four references had drifted across three unrelated merges. Two were
refreshed with #186; these are the other two.

Each recorded two changes, not one. `app-sidebar` lost Jobs (#27,
shipped) and moved its highlight from Home to Tracks; `now-playing`
gained the source line (shipped) and was playing from "a dynamic mix".
Both are singleton stores read by a case that sets nothing, so the shot
photographs whatever the case above it left behind — blessing that
would have pinned the file's own ordering into a PNG. Both cases state
their world now, and only then are the references re-recorded.

The second half of the issue asks whether this tier should gate, and
the answer is measured rather than preferred: replayed in a bare
ubuntu:24.04 container — CI's `check` image — three of the ten
baselines fail on rendering alone (`track-info` and one `page-header`
shot at ratio 0.03 against a 0.02 allowance, `seek-bar` one pixel
shorter), and the two stale ones disagree about their new height
between the machines. So CI cannot run this suite without a second,
container-recorded baseline set that every local run would then fail
against, and a pre-push hook is the same fault with the machines
swapped. It stays local and opt-in; what replaces the gate is the rule
that a change moving a component's geometry refreshes that component's
baseline in the same commit, having read the image, and never one it
did not cause. Written where a person meets it: the skill's tier doc
has the table, SKILL.md has the obligation, CLAUDE.md has the
constraint.

Deleting the baselines was the third option and is declined: this tier
has caught one thing no other could, the `<span>` that lost the UA
stylesheet's `box-sizing` and grew a badge 36→38px.

Closes #196

.pi/skills/yellowjacket-dev/SKILL.md

@@ -158,7 +158,7 @@ only climb when it cannot.
 | You changed | Run | Cost |
 |---|---|---|
 | A Lit component, a store, the shortcut service | `make ui-test` | ~2 s, no app |
-| …and it renders differently | `make ui-visual` | + 6 baselines, opt-in |
+| …and it renders differently | `make ui-visual` | + 10 baselines, opt-in, never gates |
 | Any Go code | `make test` | 3 passes, ~2 min |
 | A service that emits events | `make test` — assert on the payload, see `backend/queue/emit_test.go` | in-process, no app |
 | A bound method or a bound struct field | `make bindings` then `make ui-test` | ~1.5 s + 2 s |
@@ -180,6 +180,13 @@ less than it looks.)
 
 Two rules about climbing:
 
+- **If you moved a component's geometry, run `make ui-visual` and
+  refresh that component's baseline in the same commit.** Nothing else
+  will: it is the one tier in this repo no hook and no CI job runs, and
+  it cannot be one — its references are machine-specific, measured in
+  [references/ui-tier.md](references/ui-tier.md). Four of them drifted
+  across three merges before anyone noticed (#196). Read the image;
+  never bless a reference you did not cause.
 - **A component test passing is not the app rendering.** If you touched
   anything in `frontend/src`, verify it in the real app too — start it
   headless, `screenshot --filename=/tmp/shot.png`, and *read the PNG*.

.pi/skills/yellowjacket-dev/references/ui-tier.md

@@ -78,9 +78,58 @@ synchronously.
   Microtasks and not a timer, deliberately: a timer hangs forever under
   the suites that install fake ones.
 
-Visual baselines are font-hinting and compositing sensitive, which is
-why they are opt-in: they only mean anything on the machine that
-recorded them.
+## The visual tier does not gate, and that is measured (#196)
+
+`make ui-visual` is the same suite with nine `toMatchScreenshot`
+baselines switched on. **Nothing runs it but a person**, deliberately,
+and the reason is a number rather than a preference: the committed
+baselines were recorded on Arch, and replayed in a bare `ubuntu:24.04`
+container — CI's `check` image — three of them fail for reasons that
+have nothing to do with any component.
+
+| baseline | Arch | ubuntu:24.04 |
+|---|---|---|
+| `page-header` filtered-by-search | passes | ratio 0.03 differ, against a 0.02 allowance |
+| `track-info` | passes | ratio 0.03 differ |
+| `seek-bar` | 1152×18 | 1152×17 |
+
+The two references that were genuinely stale did not even agree about
+their *new* size — `now-playing` renders 1152×65 on Arch and 1152×64 in
+the container. So moving CI's `check` job from `make ui-test` to
+`make ui-visual` is not a one-line change: it needs a second,
+container-recorded baseline set, which every local run would then fail
+against. That is the same trap the other way round, and a pre-push hook
+is the same fault again — one machine's baselines against everybody
+else's renderer.
+
+So the tier stays local and opt-in, and the rule that replaces the gate
+is:
+
+- **A change that moves a component's geometry refreshes that
+  component's reference in the same commit, having read the image.**
+  Look at the PNG; the dimensions in the failure message are the cheap
+  half of the answer.
+- **Never refresh a reference you did not cause.** #196 exists because
+  four of them drifted across three unrelated merges, and every red run
+  made the next person likelier to stop running the tier than to read
+  it.
+- **State the world the shot is taken in.** The stores are singletons,
+  so a visual case that sets nothing photographs whatever the previous
+  case left behind — which is how the sidebar's baseline came to have
+  Tracks lit and `now-playing`'s to be playing from a dynamic mix.
+- **`make ui-visual-update UI_ARGS=<path>` does not filter** and
+  re-records *every* baseline, blessing any stale one in silence:
+  vitest's `--update` takes the following positional as its value. Until
+  #204 lands, record one file with
+  `cd frontend && YJ_VISUAL=1 npx vitest run --update=true <path>`, and
+  check `git status` before committing either way.
+
+What the tier is worth, for the record: it is a *layout* check, blind to
+colour (the component tier has no `:root`, so it renders the fallbacks —
+`make ui-visual` passed unchanged through a whole palette rewrite,
+twice), and it has caught one thing nothing else could — swapping
+`library-status-indicator`'s `<button>` for a `<span>` lost the UA
+stylesheet's `box-sizing` and grew the badge 36→38px.
 
 ## Bindings