feat(plex): playlist bulk add/remove + group-aware playlist cards

Add POST /playlists/{id}/items/bulk and /items/remove-bulk so a whole
season or show can be added/removed in one call (input order preserved,
duplicates skipped). Extend GET /playlists with contains_group=<rk,rk,…>
returning per-playlist group_in + a top-level group_size for the bulk
add-to-playlist dialog. Include the show's rating_key (show_id) on
playlist episode cards so the client can group a playlist by show/season.

backend/app/routes/plex.py

@@ -186,11 +186,15 @@ def _episode_card(e: PlexItem, st: PlexState | None) -> dict:
     }
 
 
-def _leaf_card(it: PlexItem, st: PlexState | None, show_title: str | None = None) -> dict:
-    """A playable-leaf card (movie or episode). Used by playlists, which can mix both kinds."""
+def _leaf_card(
+    it: PlexItem, st: PlexState | None, show_title: str | None = None, show_rk: str | None = None
+) -> dict:
+    """A playable-leaf card (movie or episode). Used by playlists, which can mix both kinds.
+    `show_rk` (the show's rating_key) lets the client group a playlist's episodes by show/season."""
     if it.kind == "episode":
         card = _episode_card(it, st)
         card["show_title"] = show_title
+        card["show_id"] = show_rk
         return card
     return _movie_card(it, st)
 
@@ -639,15 +643,23 @@ def _playlist_item_query(db: Session, pid: int):
 @router.get("/playlists")
 def playlists(
     contains: str | None = None,
+    contains_group: str | None = None,
     user: User = Depends(current_user),
     db: Session = Depends(get_db),
 ) -> dict:
     """The current user's playlists (newest-touched first), each with an item count + a cover thumb.
-    `contains`=an item rating_key adds `has_item` per playlist (for the 'add to playlist' dialog)."""
+    `contains`=an item rating_key adds `has_item` per playlist (for the single 'add to playlist' dialog).
+    `contains_group`=a comma-separated list of rating_keys adds `group_in` per playlist (how many of the
+    group it already holds) + a top-level `group_size`, for the 'add a whole season/show' dialog."""
     contains_id = None
     if contains:
         row = db.query(PlexItem.id).filter_by(rating_key=str(contains)).first()
         contains_id = row[0] if row else None
+    group_ids: set[int] | None = None
+    if contains_group is not None:
+        rks = [s for s in (contains_group or "").split(",") if s]
+        rows = db.query(PlexItem.id).filter(PlexItem.rating_key.in_(rks or [""])).all()
+        group_ids = {r[0] for r in rows}
     out = []
     for pl in db.query(PlexPlaylist).filter_by(user_id=user.id).order_by(PlexPlaylist.updated_at.desc()):
         count = db.query(func.count(PlexPlaylistItem.id)).filter_by(playlist_id=pl.id).scalar() or 0
@@ -658,8 +670,18 @@ def playlists(
                 db.query(PlexPlaylistItem.id).filter_by(playlist_id=pl.id, item_id=contains_id).first()
                 is not None
             )
+        if group_ids is not None:
+            card["group_in"] = (
+                db.query(func.count(PlexPlaylistItem.id))
+                .filter(PlexPlaylistItem.playlist_id == pl.id, PlexPlaylistItem.item_id.in_(group_ids or [0]))
+                .scalar()
+                or 0
+            )
         out.append(card)
-    return {"playlists": out}
+    resp: dict = {"playlists": out}
+    if group_ids is not None:
+        resp["group_size"] = len(group_ids)
+    return resp
 
 
 @router.post("/playlists")
@@ -694,10 +716,18 @@ def playlist_detail(pid: int, user: User = Depends(current_user), db: Session =
         )
     }
     shows = {
-        sh.id: sh.title
+        sh.id: sh
         for sh in db.query(PlexShow).filter(PlexShow.id.in_([it.show_id for it in items if it.show_id] or [0]))
     }
-    cards = [_leaf_card(it, states.get(it.id), shows.get(it.show_id)) for it in items]
+    cards = [
+        _leaf_card(
+            it,
+            states.get(it.id),
+            shows[it.show_id].title if it.show_id in shows else None,
+            shows[it.show_id].rating_key if it.show_id in shows else None,
+        )
+        for it in items
+    ]
     return {"id": pl.id, "title": pl.title, "items": cards}
 
 
@@ -748,6 +778,65 @@ def playlist_remove_item(pid: int, item_rating_key: str, user: User = Depends(cu
     return {"ok": True}
 
 
+def _items_by_rks(db: Session, rks: list) -> list[PlexItem]:
+    """Resolve rating_keys to PlexItems, preserving the input order (drops unknown keys)."""
+    order = [str(k) for k in rks if str(k)]
+    if not order:
+        return []
+    by_rk = {it.rating_key: it for it in db.query(PlexItem).filter(PlexItem.rating_key.in_(order))}
+    seen: set[str] = set()
+    out: list[PlexItem] = []
+    for rk in order:
+        it = by_rk.get(rk)
+        if it is not None and rk not in seen:
+            seen.add(rk)
+            out.append(it)
+    return out
+
+
+@router.post("/playlists/{pid}/items/bulk")
+def playlist_add_bulk(pid: int, payload: dict, user: User = Depends(current_user), db: Session = Depends(get_db)) -> dict:
+    """Append many items at once (a whole season/show). Already-present items are skipped; the input
+    order is preserved for the newly-added ones. Returns how many were added + the new total."""
+    pl = _own_playlist_or_404(db, pid, user)
+    items = _items_by_rks(db, payload.get("item_rating_keys") or [])
+    existing = {row[0] for row in db.query(PlexPlaylistItem.item_id).filter_by(playlist_id=pid)}
+    pos = int(db.query(func.coalesce(func.max(PlexPlaylistItem.position), -1)).filter_by(playlist_id=pid).scalar())
+    added = 0
+    for it in items:
+        if it.id in existing:
+            continue
+        pos += 1
+        db.add(PlexPlaylistItem(playlist_id=pid, item_id=it.id, position=pos))
+        existing.add(it.id)
+        added += 1
+    if added:
+        pl.updated_at = datetime.now(timezone.utc)
+    db.commit()
+    total = db.query(func.count(PlexPlaylistItem.id)).filter_by(playlist_id=pid).scalar() or 0
+    return {"added": added, "item_count": total}
+
+
+@router.post("/playlists/{pid}/items/remove-bulk")
+def playlist_remove_bulk(pid: int, payload: dict, user: User = Depends(current_user), db: Session = Depends(get_db)) -> dict:
+    """Remove many items at once (a whole season/show, or a multi-select). Returns how many were
+    removed + the new total."""
+    pl = _own_playlist_or_404(db, pid, user)
+    ids = [it.id for it in _items_by_rks(db, payload.get("item_rating_keys") or [])]
+    removed = 0
+    if ids:
+        removed = (
+            db.query(PlexPlaylistItem)
+            .filter(PlexPlaylistItem.playlist_id == pid, PlexPlaylistItem.item_id.in_(ids))
+            .delete(synchronize_session=False)
+        )
+        if removed:
+            pl.updated_at = datetime.now(timezone.utc)
+    db.commit()
+    total = db.query(func.count(PlexPlaylistItem.id)).filter_by(playlist_id=pid).scalar() or 0
+    return {"removed": removed, "item_count": total}
+
+
 @router.put("/playlists/{pid}/order")
 def reorder_playlist(pid: int, payload: dict, user: User = Depends(current_user), db: Session = Depends(get_db)) -> dict:
     """Set the playlist order from an explicit list of item rating_keys (0-based positions)."""