refactor(ipc): consume generated bindings for library catalog/genre reads

FE cutover for the D1 slice: libraryGetCatalogYearBounds and
libraryGetGenreAlbumCounts now call the generated commands.* bindings instead of
a hand-written invoke<T>('cmd', ...), unwrapping the specta Result union (rethrow
on error — behavior-preserving). The duplicated hand DTOs collapse into named
aliases of the generated CatalogYearBoundsDto / GenreAlbumCountDto, so the shape
lives in one place (the contract) and consumers stay unchanged.

Verified the guard end to end: a serde-rename of the Rust field (contract change,
Rust still compiles) regenerated bindings and made tsc fail at the FE consumer;
reverted. cargo + tsc now enforce this slice's contract at compile time.

src/lib/api/library/dto.ts

@@ -4,6 +4,7 @@
  * `lib/api/library.ts` god-module; the wrappers (reads/sync/stats/events) and the
  * `@/lib/api/library` barrel re-export these, so consumers are unchanged.
  */
+import type { CatalogYearBoundsDto, GenreAlbumCountDto } from '@/generated/bindings';
 
 export interface TrackRefDto {
   serverId: string;
@@ -363,16 +364,10 @@ export type PlaySessionYearBounds = {
   maxYear: number | null;
 };
 
-export type CatalogYearBounds = {
-  minYear: number | null;
-  maxYear: number | null;
-};
-
-export type GenreAlbumCountRow = {
-  value: string;
-  albumCount: number;
-  songCount: number;
-};
+// Sourced from the tauri-specta contract (single source of truth); kept as named
+// aliases so existing consumers stay unchanged while the shape lives in one place.
+export type CatalogYearBounds = CatalogYearBoundsDto;
+export type GenreAlbumCountRow = GenreAlbumCountDto;
 
 export type LibraryGenreAlbumsRequest = {
   serverId: string;

src/lib/api/library/stats.ts

@@ -4,6 +4,7 @@
  * `@/lib/api/library` barrel.
  */
 import { invoke } from '@tauri-apps/api/core';
+import { commands } from '@/generated/bindings';
 import { serverIndexKeyForId, mapServerIdFromIndexKey } from './internal';
 import type {
   CatalogYearBounds,
@@ -19,22 +20,23 @@ import type {
   PlaySessionRecentTrack,
 } from './dto';
 
-export function libraryGetCatalogYearBounds(args: { serverId: string }): Promise<CatalogYearBounds> {
+export async function libraryGetCatalogYearBounds(args: {
+  serverId: string;
+}): Promise<CatalogYearBounds> {
   const indexKey = serverIndexKeyForId(args.serverId);
-  return invoke<CatalogYearBounds>('library_get_catalog_year_bounds', {
-    serverId: indexKey,
-  });
+  const res = await commands.libraryGetCatalogYearBounds(indexKey);
+  if (res.status === 'error') throw new Error(res.error);
+  return res.data;
 }
 
-export function libraryGetGenreAlbumCounts(args: {
+export async function libraryGetGenreAlbumCounts(args: {
   serverId: string;
   libraryScope?: string;
 }): Promise<GenreAlbumCountRow[]> {
   const indexKey = serverIndexKeyForId(args.serverId);
-  return invoke<GenreAlbumCountRow[]>('library_get_genre_album_counts', {
-    serverId: indexKey,
-    libraryScope: args.libraryScope,
-  });
+  const res = await commands.libraryGetGenreAlbumCounts(indexKey, args.libraryScope ?? null);
+  if (res.status === 'error') throw new Error(res.error);
+  return res.data;
 }
 
 /** Paginated albums for one genre from the local track index. */