fix(explore): scroll the album page as one on a phone

`explore-album-details` was a fixed header over a scrolling tracklist,
which is the desktop arrangement. At the reference device's 424x439 the
header owned 253 of the panel's 318px and the list scrolled inside the
64 that were left, and the header's flex row squeezed `.album-info` to
112px beside a 200px cover -- so the title drew as one ellipsised glyph
and two of the album's three primary actions were clipped by the
component's own `overflow: hidden`: "Shuffle album" ended at x=443 in a
424px box, reachable by no gesture.

Below 600px the host is the scroller and `.content` stops being one, so
the header scrolls away and the page moves together; the header stacks
art over info, so the info column has the row's whole width. The
tracklist is plain DOM rather than a virtualizer, so nothing inside
wants a scroll window of its own.

Another `min-width: 0` was not the fix and the issue's own measurement
says so: `.album-info` carries one and was shrinking as asked. Nor
could `layout-overflow.spec.ts` see any of this -- `body.scrollWidth`
equalled the viewport throughout, because the overflow was inside a
component -- so the new spec measures each header control against the
host's own box, which is `top-bar-fit.spec.ts`'s shape for the same
reason.

The phone block is last in the stylesheet on `index.css`'s rule: a
media query adds no specificity, so above the rules it overrides every
declaration in it would be silently dead.

Closes #66

frontend/src/components/explore-album-details/explore-album-details.ts

@@ -892,6 +892,67 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
             .track-row .track-request {
                 flex-shrink: 0;
             }
+
+            /* ── The phone (#66) ──
+             *
+             * **This block is last on purpose**, for index.css's
+             * reason: a media query adds no specificity, so a rule
+             * written above the plain one it overrides loses to it and
+             * every declaration here is silently dead.
+             *
+             * Two faults, one shape. The page is a fixed header over a
+             * scrolling tracklist — the desktop arrangement — so at the
+             * reference device's 424x439 the header owned 253 of the
+             * panel's 318px and the tracklist scrolled inside the 64px
+             * that were left. And the header's flex row squeezed
+             * .album-info to 112px, so the title drew as one ellipsised
+             * glyph and two of the album's three primary actions were
+             * clipped by the host's own overflow: Shuffle album ended
+             * at x=443 in a 424px box, unreachable by any gesture.
+             *
+             * .album-info carries min-width: 0 and was shrinking as
+             * asked, so another one is not the fix — the row has to
+             * stack, or the info column has nothing to be wide with.
+             *
+             * The scroller moves to the host and .content stops being
+             * one, which is what makes the header scroll away; the
+             * tracklist is plain DOM rather than a virtualizer, so
+             * nothing inside wants a scroll window of its own. */
+            @media (max-width: 599px) {
+                :host {
+                    overflow-y: auto;
+                }
+
+                .album-header {
+                    flex-direction: column;
+                    align-items: flex-start;
+                    gap: 12px;
+                    padding: 12px 16px;
+                }
+
+                /* Stacked, the art is the whole of the header's width
+                 * budget and its 200px square is 45% of the reference
+                 * device's height. It is still what identifies the
+                 * album, so it shrinks rather than going. */
+                .cover-art-container {
+                    width: 140px;
+                    height: 140px;
+                }
+
+                /* A column flex item takes its content's width from
+                 * align-items: flex-start above, which would leave the
+                 * actions wrapping inside a box narrower than the row
+                 * they now have to themselves. */
+                .album-info {
+                    align-self: stretch;
+                }
+
+                .content {
+                    flex: 0 0 auto;
+                    overflow-y: visible;
+                    padding: 16px 16px 24px;
+                }
+            }
         `,
     ];