feat(playlists): manual drag order + Sort A-Z for the playlist list (#1004)

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>

lib/routers/playlists.py

@@ -70,6 +70,37 @@ def api_create_playlist(data: dict):
     return appstate.meta_db.create_playlist(name, kind=kind)
 
 
+@router.post("/api/playlists/reorder")
+def api_reorder_playlists(data: dict):
+    """Manual ordering of the playlists themselves (position = index in
+    `order`); the songs-within sibling is /api/playlists/{pid}/reorder.
+    System playlists stay pinned first and are not part of the order."""
+    order = data.get("order")
+    if not isinstance(order, list) or not all(
+            isinstance(i, int) and not isinstance(i, bool) for i in order):
+        return JSONResponse({"error": "order must be a list of playlist ids"}, status_code=400)
+    # Require an exact permutation of the current non-system playlist ids: a
+    # list with duplicates, omissions, extras, unknown ids, or a system id
+    # would otherwise produce duplicate positions / a partial reorder while
+    # still returning 200 (mirrors the songs-within validation).
+    current = [p["id"] for p in appstate.meta_db.list_playlists() if not p["system_key"]]
+    if len(order) != len(current) or sorted(order) != sorted(current):
+        return JSONResponse(
+            {"error": "order must be a permutation of your playlists' ids"},
+            status_code=400,
+        )
+    appstate.meta_db.reorder_playlists(order)
+    return api_list_playlists()
+
+
+@router.post("/api/playlists/sort-alpha")
+def api_sort_playlists_alpha():
+    """Clear every manual playlist position → back to the alphabetical
+    default (system playlists were pinned first either way)."""
+    appstate.meta_db.clear_playlist_positions()
+    return api_list_playlists()
+
+
 @router.get("/api/playlists/{pid}")
 def api_get_playlist(pid: int):
     pl = appstate.meta_db.get_playlist(pid)