docs: record the a11y tail, and four names written where nothing reads

Phase 3 shipped in six landings and a11y.md is closed, which closes all
four audits from 2026-08-11.

The pass's one lesson is that an accessible name is computed on the
element carrying the role, and every tier we check with looks somewhere
else: the audit read the source and credited a name that was never
computed, an AX sweep read the tree and reported a placeholder-only box
as clean, and a component test asserted the attribute and pinned the
bug it existed to prevent.

Six of the audit's claims turned out to be wrong or smaller than
written, and one of the plan's own findings was false — the page
header's sort control is named on all nine views. All of them are
written down, which is where a third of the value of the last two plans
came from.

CLAUDE.md

@@ -130,7 +130,7 @@ meaningless against the seed's one empty playlist, so it builds ten
 It wraps every bound Go method, so "did that refetch the library" is a
 fact rather than an inference. It is not a spec and does not run in CI.
 
-**The cheapest tier needs none of that.** `make ui-test` runs 480
+**The cheapest tier needs none of that.** `make ui-test` runs 672
 Vitest tests in a real Chromium in ~2 s with no Wails, no backend, no
 seeded library and no virtual display, because `frontend/wailsjs/` is a
 pure passthrough to `window.go` / `window.runtime` and
@@ -586,6 +586,76 @@ only ever moved by an arrow key, so a row reached by a click or by Tab
 left it at 0 and `Enter` played the first track in the queue from any
 focused row.
 
+**A name is computed where the role is, and that is rarely where you
+wrote it.** Four surfaces wrote a name somewhere the accessibility tree
+never looked. `wa-slider` puts `role="slider"` on a div in its own
+shadow root pointing `aria-labelledby` at an empty internal `<label>`,
+which outranks the host's `aria-label` — so both sliders computed a
+name of `""`, and `a11y.md` lists both under *what is already correct*.
+The name comes from `label` now, the library's own API, and
+`styles/wa-slider-label.css.ts` hides it: preferred over reaching into
+the shadow root the way `name-dialog.ts` must, because if Web Awesome
+renames the part the label becomes *visible and correctly named*
+rather than silently nameless. Its second rule is load-bearing —
+`#slider` takes an 8px margin the moment a label exists, which grows
+the bar 6px → 14px and moves the transport with it.
+`wa-progress-bar`'s `label` *is* an `aria-label` and is invisible, so
+there it is just the right attribute.
+
+The same thing in the light DOM: `config-field` rendered a `<label>`
+as a **sibling** with no `for`, so **24 of 93 controls on Settings**
+computed an empty name. They use `for`/`id` (a fixed id, safe only
+because each field is its own shadow root) rather than `aria-label`,
+for what it buys beyond the name — the label text becomes a click
+target. And three surfaces are named but identify nothing, which is
+the same fault one step milder: three shortcut buttons announced
+themselves as "S", thirty-six column arrows as "Move up", and every
+queue row's remove button as "Remove from queue".
+
+**Checking any of this needs the browser's own answer, and "0 unnamed"
+is not it.** A `placeholder` is an accname fallback, so an
+`Accessibility.getFullAXTree` sweep of all eleven views reported
+Explore's search box — the audit's own `a11y.26` — as clean. A sweep
+for *empty* names cannot see a *weak* one.
+
+**The shell scrolls sideways and not down.** `body` is
+`overflow-x: auto; overflow-y: hidden`, and both halves are measured.
+Vertically there is nothing to fix: the middle grid row is `1fr` and
+absorbs the 4em bars exactly — at 200% text on an 800×600 window the
+bars go 64 → 128px, the main panel 472 → 344px, and the footer still
+lands on 600. Horizontally the shell is 784px inside a 320px viewport
+(400% page zoom, the width WCAG 1.4.10 names) and 464px of it,
+including the job indicator and the queue button, used to sit behind
+`overflow: hidden`. Keeping the vertical axis fixed is what keeps the
+transport where a desktop player's transport belongs. At every size
+this app promises, no scrollbar appears. Note that `overflow: hidden`
+still permits *programmatic* scrolling, so a probe that sets
+`scrollLeft` passes on the broken build; the spec uses a wheel gesture.
+
+**The playing row is a shape, not a hue.** `track-list` and
+`queue-panel` draw a `::before` triangle in each row's own left
+padding, plus `aria-current` — before, both rows were a background tint
+and a text colour and nothing else (WCAG 1.4.1). It is in the padding
+because the track list's grid columns are computed from the host width,
+so a marker in the flow moves every cell on the playing row and nothing
+else. Both tiers assert it is **absent** on the other rows: a marker
+that renders everywhere satisfies "the playing row has one" for free.
+One thing to know before checking it — a track started from the *track
+list* leaves the queue's `currentIndex` at −1, so the panel has no
+current row at all in that flow, which reads exactly like the marker
+not working.
+
+**The first thing Tab reaches is a skip link.** Two details are
+load-bearing and neither is the link's text. It is `position: absolute`
+in **both** states, because `body` is a grid with named areas and an
+in-flow extra child is auto-placed into one of them. And `<main>`
+carries `tabindex="-1"`, or the fragment moves the scroll, leaves the
+tab sequence exactly where it was, and looks like it worked. The
+subtitle beside it is a `<p>`, which is also what an `hgroup` is
+supposed to contain — and dropping the `<h3>`'s bottom margin shortened
+the flex-centred title block enough to move it down into the 4em bar's
+clip, so `.title` zeroes both margins.
+
 **A selectable grid is a listbox.** The four grids that ctrl/shift-select
 (`artists-view`, `genres-view`, `cover-grid`, and the queue) are
 `role="listbox" aria-multiselectable` over `role="option"` cards, not