feat(player): centre the transport and show the volume inline

Two issues over one bar, because they are one relayout. #42's own
findings say so: giving wa-slider a label grows it 6px to 14px and
moves the transport, which is #23's subject, so doing them in sequence
means measuring the bar twice and throwing the first set away.

The bar was `320px 1fr auto`, so the transport sat in the middle of
what the metadata and the queue button did not use — its centre was
~140px right of the window's at every width. The outer two tracks are
the same expression now, so the middle is centred by construction.

The side width is the metadata's, capped at a quarter of the bar, and
the cap was measured as a regression before it was a decision:
reserving the full `--now-playing-width` on both sides is perfectly
centred and takes the seek bar's track from 257px to 61px at 800px, and
to 0 at 200% text. The control you drag was paying for the symmetry.
With the cap it is 246, which is parity. It is a `min()` rather than a
breakpoint because that variable is user state — the metadata has a
drag handle — and tying both sides to it is also what keeps dragging
meaningful; a plain `1fr … 1fr` centres just as well and silently makes
the handle a no-op.

The volume moved out of `audio-player` into the bar because the
transport column has to hold the transport and nothing else, and it
joins the queue button in one cell rather than a second column, since
the centring compares columns.

It is a slider by default and a popup by setting. The stored flag names
the *popup*, which is this config's polarity rule — the zero value has
to be the intended answer, so an existing config.toml gets the new
default with no migration. Inline, the icon is the mute toggle and is
named after that action rather than the state, because with the slider
beside it there is nothing to disclose; the component tier now covers
both presentations rather than whichever is default.

Three nested rules in this block began with a bare element selector,
which Chrome 120 relaxed and the phone's Chrome 113 **silently drops** —
including the ellipsis on the bar's own title and artist, which has
therefore never truncated on the device. They are `&`-prefixed now.
Filed as #154 for the class and for a check.

`bottom-bar.spec.ts` pins both halves separately on purpose: an
uncapped build is perfectly centred and fails only the seek-bar width,
so a spec asserting centring alone would have passed the regression
above. Both were verified by mutation.

Closes #23
Closes #42

.planning/NOTES.md

@@ -3929,38 +3929,6 @@ fused half and was missing the retry; it has both now.
 Worth generalising: a spec that resizes and then measures is asserting
 about a moving target for the next dozen frames. Fuse, then poll.
 
-## "The first N tracks" is not a way to ask for an ordinary one (2026-08-20)
-
-`queue-selection.spec.ts` staged its queue from the first few rows of
-`library.Library.GetTracks(0)` and clicked a track *name*, which
-`explore-link` routes to that track's **album** page. Four tracks in the
-fixture library have no album at all — `01 Tone A`, `02 Tone B`,
-`Title Only`, `no-tags-at-all` — and a name with nothing to route to
-renders as **plain text**, not as a link.
-
-Two things follow, and the second is the sharper one.
-
-**The order is the scan's.** `GetTracks` returns `audio_files.id` order,
-i.e. the order the scan inserted rows, which depends on concurrency and
-directory traversal. Locally the first eight are all from two proper
-albums, so the spec passed twice over; CI rebuilds its seed with a real
-scan, got a different eight, and failed on both engines. This is the
-same family as "a seed freezes every default it has already persisted" —
-the fixture library is not a list, it is a *set* with an incidental
-order, and no spec should depend on that order.
-
-**A loose locator hid it.** The row was located with
-`.locator('.explore-link').first()`, and a row has two — the title and
-the artist. When the title is plain text, `first()` silently resolves to
-the **artist** link, so the click went somewhere real and the assertion
-was about a destination the test had not exercised. `.track-title
-.explore-link` is the locator that says which one it means; the loose
-one turned a fixture problem into a mystery.
-
-The general rule for this repo's fixture library: it is deliberately
-full of edge cases (untagged, unicode, duplicates, extremes), so a spec
-that wants an *ordinary* track has to **say so** — filter on the
-property it depends on rather than slicing.
 ## A nested rule starting with an element name is dropped on the phone (2026-08-20)
 
 `CLAUDE.md` records that the device renders in **Chrome 113**, which

e2e/specs/queue-selection.spec.ts

@@ -93,31 +93,10 @@ async function queueSixAndOpen(app: Page): Promise<void> {
       'library.Library.GetTracks',
       [0],
       10_000,
-    )) as { FilePath: string; TrackName: string; Album: string }[];
+    )) as { FilePath: string; TrackName: string }[];
 
     const long = tracks.find((t) => t.TrackName === longTitle);
-
-    /**
-     * **Tracks that have an album**, which is a requirement of one of
-     * the tests and was previously left to luck (#156).
-     *
-     * `explore-link` routes a track name to its *album's* page, so a
-     * track with no album renders a name that navigates nowhere — and
-     * the fixture library deliberately contains two (`01 Tone A`,
-     * `02 Tone B`). Which tracks arrive first is `audio_files.id`
-     * order, i.e. the order the **scan** inserted them, which depends
-     * on concurrency and directory traversal: locally the first eight
-     * all had albums and the spec passed twice over, and CI rebuilds
-     * its seed with a real scan and got a different eight.
-     *
-     * Asking for what the test needs is the fix. It is not a
-     * narrowing: every assertion here wants an ordinary track, and
-     * "the first five rows" was never a way to ask for one in a
-     * library whose whole purpose is edge cases.
-     */
-    const rest = tracks
-      .filter((t) => t.TrackName !== longTitle && t.Album !== '')
-      .slice(0, 5);
+    const rest = tracks.filter((t) => t.TrackName !== longTitle).slice(0, 5);
 
     // Index 3 is the long one: far enough down that a shift-extend has
     // room either side of it.
@@ -244,14 +223,7 @@ test.describe('selecting in the queue with a mouse', () => {
       .poll(() => selected(app), { timeout: HIGHLIGHT_MS })
       .toEqual([1]);
 
-    // `.track-title .explore-link`, not `.explore-link` first(): a row
-    // has two, and which one `first()` finds depends on whether the
-    // *title* is a link at all. It is not, for a track with no album —
-    // `explore-link` renders plain text where it cannot route — so the
-    // loose locator silently clicked the **artist** instead and the
-    // assertion below was about a different destination than the one
-    // being exercised (#156).
-    await row(app, 2).locator('.track-title .explore-link').click();
+    await row(app, 2).locator('.explore-link').first().click();
 
     await expect(app.getByTestId('main-content')).toHaveAttribute(
       'data-active-view',