chore(eslint): add ESLint toolchain and clean src to strict 0/0 (#1165)

* chore(eslint): add eslint toolchain and configs

* fix(eslint): resolve gradual-config errors (rules-of-hooks, no-empty, prefer-const, …)

* chore(eslint): clear unused vars in config, contexts, app and test

* chore(eslint): clear unused vars in api and music-network

* chore(eslint): clear unused vars in utils

* chore(eslint): clear unused vars in store

* chore(eslint): clear unused vars in cover and hooks

* chore(eslint): clear unused vars in components

* chore(eslint): clear unused vars in pages

* chore(eslint): remove explicit any in src

* chore(eslint): align react-hooks exhaustive-deps

* chore(eslint): zero gradual config on src

* chore(eslint): strict hook rules in store and utils

* chore(eslint): strict hook rules in hooks and cover

* chore(eslint): strict hook rules in components

* chore(eslint): strict hook rules in pages and contexts

* chore(eslint): document scripts ignore in eslint config

* chore(eslint): add lint script and zero strict findings

* chore(eslint): address review round 1 (gradual 0/0, per-site disable reasons)

* chore(eslint): tighten two set-state disable comments (review round 2 LOW)

* chore(nix): sync npmDepsHash with package-lock.json

* docs(changelog): add Under the Hood entry for ESLint setup (PR #1165)

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

src/contexts/DragDropContext.tsx

@@ -53,6 +53,10 @@ const Ctx = createContext<DragDropContextValue>({
   isDragging: false,
 });
 
+// useDragDrop / useDragSource / registerQueueDragHitTest are the documented
+// drag-drop API surface, intentionally co-located with DragDropProvider; this
+// HMR-only rule does not warrant fragmenting the context module.
+// eslint-disable-next-line react-refresh/only-export-components
 export const useDragDrop = () => useContext(Ctx);
 
 function isQueueReorderDrag(data: string): boolean {
@@ -70,6 +74,8 @@ const queueDragHitTests: Array<(x: number, y: number) => boolean> = [];
  * Register a function that returns true when (clientX, clientY) lies inside
  * this window’s queue drop area. Unregister on cleanup.
  */
+// Part of the drag-drop API co-located with the provider (see note above).
+// eslint-disable-next-line react-refresh/only-export-components
 export function registerQueueDragHitTest(fn: (x: number, y: number) => boolean): () => void {
   queueDragHitTests.push(fn);
   return () => {
@@ -154,6 +160,8 @@ export function DragDropProvider({ children }: { children: React.ReactNode }) {
   });
 
   const stateRef = useRef(state);
+  // React Compiler refs rule: latest-value box kept in sync for use in callbacks; not render data.
+  // eslint-disable-next-line react-hooks/refs
   stateRef.current = state;
 
   const startDrag = useCallback(
@@ -277,10 +285,14 @@ const DRAG_THRESHOLD = 5; // px before drag starts
  * Returns an onMouseDown handler for a draggable element.
  * Usage:  <div {...useDragSource(payload)} />
  */
+// Part of the drag-drop API co-located with the provider (see note above).
+// eslint-disable-next-line react-refresh/only-export-components
 export function useDragSource(getPayload: () => DragPayload) {
   const { startDrag } = useDragDrop();
   const startPosRef = useRef<{ x: number; y: number } | null>(null);
   const payloadRef = useRef(getPayload);
+  // React Compiler refs rule: latest-value box kept in sync for use in handlers; not render data.
+  // eslint-disable-next-line react-hooks/refs
   payloadRef.current = getPayload;
 
   const onMouseDown = useCallback(