Playlists could only ever be listed alphabetically (system playlists first).
Users who group playlists by purpose had no way to put the ones they reach
for daily at the front.
Adds a nullable `position` column and orders by
`(system_key IS NULL), (position IS NULL), position, name COLLATE NOCASE`,
so manually-ordered playlists lead, unpositioned ones keep sorting
alphabetically behind them, and system playlists stay pinned first.
Drag-reorder mirrors the existing within-playlist song reorder, adapted for
grid tiles (insert side decided on the horizontal midpoint since tiles flow
left-to-right then wrap). System playlists are neither drag sources nor drop
targets. `POST /api/playlists/reorder` requires an exact permutation of the
current non-system ids, so a duplicate, omission, extra, unknown id, or a
system id is rejected rather than silently producing duplicate positions;
booleans are rejected explicitly because `sorted([True, 2]) == sorted([1, 2])`
would otherwise slip through the permutation check.
`POST /api/playlists/sort-alpha` clears the manual order again.
Claude-Session: https://claude.ai/code/session_01SFDokqh2H6mEjk1Kgbi6JW
Signed-off-by: ChrisBeWithYou <christian.a.cowan@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>