feat(explore): mark what is not owned, everywhere it can be shown

`explore-album-details` had the rule right for one tracklist and
nothing else did: Explore's cards, `top-results-row` and the artist
page's three card shapes all mixed owned and unowned with a small badge
as the only difference, and drew a green tick on the *common* case —
which is the treatment that tracklist's own green ticks were removed
for.

`utils/ownership.ts` is the rule written once, so eight call sites
stop each holding their own version:

- owned is plain, and draws no badge at all;
- unowned is dimmed *and* says so in its accessible name, because
  dimming is a colour and cannot be the only signal;
- a partly-held album says how partly.

**Ownership is a file, and `localId` is the flag that says so.** The
album page answers with `filePaths`, a real file per displayed track; a
card grid cannot afford that and does not need to, because
`local_*_id` is built by queries that all join `audio_files` and
cleared by a prune whose existence test is a file test in every case.
`inLibrary` is written by the same pass, so the two agree in a healthy
database — but it is a one-way ratchet (`MAX(in_library, excluded)`)
whose only clearing pass is gated on a non-null local id, so it cannot
be un-set on its own.

Where they already diverged was the client. Both `explore-view` and
`explore-artist-details` kept a `libraryMBIDs` set that accumulated
every MBID ever seen with `inLibrary` and cleared it never, in views
that never unmount. Both are deleted.

And one card answered the question twice and got two answers:
`renderReleaseMenuItems` gates Play on `localId > 0` while the badge
and `albumTarget.owned` used `inLibrary`, so an album with the flag and
no local row drew a tick saying it was in your library, offered no
Play, and — the request item being gated on *not* owned — offered no
way to ask for it either.

The count comes from `completenessStore`, shaped like `credit-store`:
`request()` is per-card and coalesces a screenful into one
`GetAlbumsCompleteness`, absence is cached as an answer, and the whole
cache is dropped on a scan, a retag or a removal rather than aged.

`aria-disabled` goes on rows that cannot be activated and deliberately
not on cards: an unowned card still navigates to the catalog page for
it, which is a perfectly good thing to do with something you do not
own.

Audited and unchanged: `home-view`, `downloads-view`, `cover-grid`,
`artist-details` and `genre-details` cannot show catalog content, so
everything on them is owned and "owned is plain" is already what they
do. The album page's own header badge stays, because that page is about
one entity and the badge is its answer rather than a mark on one of
many.

Closes #38

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

@@ -3,6 +3,7 @@ import { customElement, property, state, query } from 'lit/decorators.js';
 import { classMap } from 'lit/directives/class-map.js';
 import { designTokens } from '../../styles/tokens.css';
 import { srOnly } from '../../styles/sr-only.css';
+import { unownedLabel, unownedStyles } from '@utils/ownership';
 import {
     LookupReleaseGroup,
     BrowseReleases,
@@ -316,6 +317,7 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
         exploreLinkStyles,
         contextMenuStyles,
         srOnly,
+        unownedStyles,
         css`
             :host {
                 display: flex;
@@ -687,20 +689,14 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
                 white-space: nowrap;
             }
 
-            /* A track the library does not have, on the pattern a
-             * streaming service uses for something it cannot play: the
-             * row stays, dimmed, so the album reads as the album rather
-             * than as the subset that happens to be here.
-             *
-             * The dimming is a colour, so it cannot be the only signal
-             * — the row also carries aria-disabled, which is what
-             * reaches anyone not seeing it.  Secondary rather than
-             * tertiary because the row's hover background is
-             * bgOverlay, which tertiary does not clear. */
-            .track-row.unowned .track-title {
-                color: var(--yj-text-secondary, #b3b3b3);
-                font-weight: 400;
-            }
+            /* The dimming itself is unownedStyles, from
+             * utils/ownership.ts, imported above.  It was written here
+             * first — this tracklist is where the treatment came from —
+             * and moved out when seven other surfaces had to draw the
+             * same thing, because two of them would otherwise have
+             * ended up drawing it slightly differently.  (No backticks or
+             * apostrophes-as-quotes here: this is inside a tagged
+             * template literal.) */
 
             /* The request control is offered on every row that has
              * something to request, and is not revealed on hover.
@@ -3273,7 +3269,7 @@ export class ExploreAlbumDetails extends LitElement implements ContextMenuHost {
                                         aria-disabled=${owned ? 'false' : 'true'}
                                         aria-label=${owned
                                             ? `Play “${track.title}”`
-                                            : `${track.title} — not in your library`}
+                                            : unownedLabel(track.title, 'track')}
                                         @dblclick=${() => this.onTrackRowDblClick(track)}
                                         @contextmenu=${(e: MouseEvent) => this.onTrackContextMenu(e, track)}
                                         @keydown=${(e: KeyboardEvent) => this.onTrackRowKeydown(e, track)}