feat(slint): dedicated For You view with artist sections

Replaces the ad-hoc For You (a single album set crammed into
HomeState.sections) with a dedicated, ordered ForYouView/ForYouState
so the tab can mix album, track, and artist carousels — closer to
Tauri's For You. Lazy-loaded once on first open.

Sections (all reuse existing cards, no new card components):
  - Release Watch (album Carousel) — get_release_watch.
  - Recently Played Tracks (SlimCarousel) — local play-history.
  - Recently Played Albums (album Carousel) — local play-history.
  - Your Top Artists (ArtistCarousel) — the user's favorite artists
    via get_favorites.
  - Artists to Follow (ArtistCarousel) — similar artists seeded from
    a few favorites via get_similar_artists, excluding ones already
    followed (Follow chip shown).

Plumbing:
  - crate::foryou controller (load/apply/artwork). Five ForYou
    artwork targets feed the dedicated models.
  - select_tab("forYou") clears HomeState.sections (the home-content
    `for` renders nothing) and the For You content comes from
    ForYouView; HomeView routes the For You tab to ForYouView and
    gains an open-artist callback (wired through AppShell).
  - ensure_for_you_loaded lazy-loads on tab open (pill, header
    dropdown, and back/forward history).
  - home.rs no longer builds a For You section set (removed the
    redundant release-watch/favorites fetch on every home load).

Still to come (next increments): Qobuz Mixes row, Radio Stations
(old card design), Spotlight hero, and the reco-DB sections (More
from library, Rediscover) — those need backend the MVP lacks or the
mix detail views.

cc

crates/qbz-slint/ui/shell/AppShell.slint

@@ -79,6 +79,9 @@ export component AppShell inherits Rectangle {
                     album-clicked(id) => {
                         root.open-album(id);
                     }
+                    open-artist(id) => {
+                        root.open-artist(id);
+                    }
                     media-action(kind, id, action) => {
                         root.media-action(kind, id, action);
                     }