refactor(playlist): G.68 — extract runPlaylistSaveMeta + 3 hooks (song search / mutations / star+rating) (#635)

Four-cut cluster. 572 → 471 LOC (−101). Each handler on the page
collapses to a one-line delegate; pure code move otherwise.

runPlaylistSaveMeta — the meta save flow (updatePlaylistMeta then
optional uploadPlaylistCoverArt + getPlaylist refresh + cover toast,
or coverRemoved → null, then metaSaved toast + closes the modal).
Takes the deps separately from the opts object so the call-site
just passes through the modal's payload.

usePlaylistSongSearch — searchOpen + searchQuery driven debounced
search against subsonic. Owns the 350 ms timeout, the filter-out
of songs already in the playlist, and the searching state. Returns
{ searchResults, setSearchResults, searching } so addSong on the
page can still drop a just-added song out of the result list.

usePlaylistSongMutations — addSong / removeSong. removeSong is
trivial (filter + setSongs + savePlaylist with prevCount).
addSong preserves the .main-content scrollTop save / requestAnimationFrame
restore trick + drops the song out of both suggestions and search
results + fires the add toast with playlist name interpolation.

usePlaylistStarRating — handleRate (local override + playerStore
userRatingOverride + setRating API) + handleToggleStar (e.stopPropagation,
local set + playerStore starredOverride + star/unstar API). Reads
starredOverrides / setStarredOverride from playerStore directly so
the page doesn't have to thread them through.

PlaylistDetail drops these direct imports (now consumed in the
hooks/utility): updatePlaylistMeta, uploadPlaylistCoverArt, search,
setRating, star, unstar, showToast, useRef. Pure code move.

src/hooks/usePlaylistStarRating.ts

@@ -0,0 +1,42 @@
+import React from 'react';
+import { setRating, star, unstar } from '../api/subsonicStarRating';
+import type { SubsonicSong } from '../api/subsonicTypes';
+import { usePlayerStore } from '../store/playerStore';
+
+export interface PlaylistStarRatingDeps {
+  ratings: Record<string, number>;
+  setRatings: React.Dispatch<React.SetStateAction<Record<string, number>>>;
+  starredSongs: Set<string>;
+  setStarredSongs: React.Dispatch<React.SetStateAction<Set<string>>>;
+}
+
+export interface PlaylistStarRatingActions {
+  handleRate: (songId: string, rating: number) => void;
+  handleToggleStar: (song: SubsonicSong, e: React.MouseEvent) => void;
+}
+
+export function usePlaylistStarRating(deps: PlaylistStarRatingDeps): PlaylistStarRatingActions {
+  const { setRatings, starredSongs, setStarredSongs } = deps;
+  const starredOverrides = usePlayerStore(s => s.starredOverrides);
+  const setStarredOverride = usePlayerStore(s => s.setStarredOverride);
+
+  const handleRate = (songId: string, rating: number) => {
+    setRatings(prev => ({ ...prev, [songId]: rating }));
+    usePlayerStore.getState().setUserRatingOverride(songId, rating);
+    setRating(songId, rating).catch(() => {});
+  };
+
+  const handleToggleStar = (song: SubsonicSong, e: React.MouseEvent) => {
+    e.stopPropagation();
+    const isStarred = song.id in starredOverrides ? starredOverrides[song.id] : starredSongs.has(song.id);
+    setStarredSongs(prev => {
+      const next = new Set(prev);
+      isStarred ? next.delete(song.id) : next.add(song.id);
+      return next;
+    });
+    setStarredOverride(song.id, !isStarred);
+    (isStarred ? unstar(song.id, 'song') : star(song.id, 'song')).catch(() => {});
+  };
+
+  return { handleRate, handleToggleStar };
+}