Consolidates duplicated logic behind shared implementations — paginated
grid tabs, focus chrome, cached remote stores, sheet selection columns,
the server artifact store and a test fixture layer — and removes code
that had become unreachable. Net reduction of about 5,500 lines with no
behaviour change.
Where a fix had landed separately in code that moved into a shared
helper, the fix was re-applied inside the helper rather than left behind
in the copy that went away.
- PaginatedCardGridTabState: the collections and playlists tabs were 95%
identical; they now supply only pageSize/fetchPage/idOf instead of each
duplicating the grid, memo, inflation budget and focus wiring.
- EtagCachedRemoteStore: the anime-lists and fribb mapping stores now share
one download/cache/isolate-parse/conditional-GET lifecycle.
- FocusableTileStateMixin manages its own initState/didUpdateWidget/dispose
instead of requiring every caller to forward three lifecycle hooks.
Also drops unused ServerCapabilities entries and dead code in
focusable_list_tile and music/track_row.
edde746