feat(settings): add folder selection for music and playlists

Add UI and logic to select music and playlists folders in settings using
tauri dialog plugin. Integrate @tauri-apps/plugin-dialog, plugin-fs, and
plugin-store in both frontend and backend. Update capabilities and
dependencies to support new plugins. Improve settings page with folder
selectors and info note for better user experience.

src/lib/stores/settings.ts

@@ -0,0 +1,74 @@
+import { LazyStore } from '@tauri-apps/plugin-store';
+import { writable, type Writable } from 'svelte/store';
+
+// Settings interface
+export interface AppSettings {
+  musicFolder: string | null;
+  playlistsFolder: string | null;
+}
+
+// Initialize the store with settings.json
+const store = new LazyStore('settings.json');
+
+// Default settings
+const defaultSettings: AppSettings = {
+  musicFolder: null,
+  playlistsFolder: null
+};
+
+// Create a writable store for reactive UI updates
+export const settings: Writable<AppSettings> = writable(defaultSettings);
+
+// Load settings from store
+export async function loadSettings(): Promise<void> {
+  const musicFolder = await store.get<string>('musicFolder');
+  const playlistsFolder = await store.get<string>('playlistsFolder');
+
+  settings.set({
+    musicFolder: musicFolder ?? null,
+    playlistsFolder: playlistsFolder ?? null
+  });
+}
+
+// Save music folder setting
+export async function setMusicFolder(path: string | null): Promise<void> {
+  if (path) {
+    await store.set('musicFolder', path);
+  } else {
+    await store.delete('musicFolder');
+  }
+  await store.save();
+
+  settings.update(s => ({
+    ...s,
+    musicFolder: path
+  }));
+}
+
+// Save playlists folder setting
+export async function setPlaylistsFolder(path: string | null): Promise<void> {
+  if (path) {
+    await store.set('playlistsFolder', path);
+  } else {
+    await store.delete('playlistsFolder');
+  }
+  await store.save();
+
+  settings.update(s => ({
+    ...s,
+    playlistsFolder: path
+  }));
+}
+
+// Get music folder setting
+export async function getMusicFolder(): Promise<string | null> {
+  return await store.get<string>('musicFolder');
+}
+
+// Get playlists folder setting
+export async function getPlaylistsFolder(): Promise<string | null> {
+  return await store.get<string>('playlistsFolder');
+}
+
+// Initialize settings on app start
+loadSettings();