Closes the Flutter half of Fable #416. Web got a generalized
system-playlist refresh kebab in d12afda; this brings Flutter to
parity instead of leaving the affordance web-only.
- PlaylistsApi.refreshSystem(variant): POST
/api/playlists/system/{for-you|discover}/refresh, maps the
underscore model variant to the hyphenated route segment,
returns the rotated playlist id.
- PlaylistCard: top-right PopupMenuButton on system playlists
with a context-labelled "Refresh For You" / "Refresh Discover"
item. Calls refreshSystem, invalidates playlistsListProvider
(which reconciles the rotated UUID + new tracks), snackbars
the result. ScaffoldMessenger captured pre-await.
- Tests: kebab present for system, absent for user playlists.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen
7a0437087a