Client half of #367. Two new Library tabs, each an index plus a drill-down.
Genres are ordered by track count rather than alphabetically. Raw ID3 carries a
long tail of one-off tags, so alphabetical would bury the handful of genres you
actually have a library's worth of. Years are grouped into decades — a flat
list of every year in a decades-deep library is a wall of numbers, and the
decade is how people actually think about it.
## Selection travels in the query string, not the path
`?g=Rock%2FPop`, not `/library/genres/Rock%2FPop`. A slash-bearing genre cannot
survive a path segment — the server sees two segments, and a hard reload
wouldn't reconstruct it through the SPA fallback either. There's a test pinning
the encoded href and another pinning that the DECODED value reaches the API.
## Why these two pages don't use svelte-query for their lists
The indexes do — fetched once per mount, so static options suffice and the
cache survives bouncing in and out of a drill-down.
The drill-down lists deliberately don't. Their selection comes from the URL and
changes WITHOUT remounting the page, and this codebase has no
reactive-query-options pattern anywhere; inventing one here would be a larger
change than the feature justifies, and one I can't exercise locally. So they
use $effect keyed on the derived selection with an explicit Load more.
The stale-response guard is a plain `let`, not $state, and that's load-bearing:
as reactive state, reading the token inside the fetch path would make the
effect depend on its own writes. Its job is to discard a late response for a
previously selected genre instead of painting it over the current one.
## Also
Added the year filter to /library/albums' contract but NOT to that page's UI —
its infinite scroll is a svelte-query infinite query, and making it react to a
filter is the same reactive-options problem. The dedicated pages cover the
capability, which is the shape the task offered as its alternative.
Library tab bar's comment claims it mirrors Android's LibraryScreen. These two
tabs have no Android equivalent, so I noted that inline rather than leaving the
claim quietly false. Parity remains an open call.
Not yet done from #367's bullet list: genre/year quick-jump links on album and
artist detail. Year is free (AlbumRef already carries it) but genre is exposed
nowhere client-side — AlbumDetail is AlbumRef + tracks, and neither carries
genre — so it needs a small API addition. Following as its own commit.
