refactor: convert download manager into a state class (#17491)

* fix(web): download progress bar not functioning

* remove unused method

web/src/lib/stores/download-store.svelte.ts

@@ -0,0 +1,51 @@
+export interface DownloadProgress {
+  progress: number;
+  total: number;
+  percentage: number;
+  abort: AbortController | null;
+}
+
+class DownloadStore {
+  assets = $state<Record<string, DownloadProgress>>({});
+
+  isDownloading = $derived(Object.keys(this.assets).length > 0);
+
+  #update(key: string, value: Partial<DownloadProgress> | null) {
+    if (value === null) {
+      delete this.assets[key];
+      return;
+    }
+
+    if (!this.assets[key]) {
+      this.assets[key] = { progress: 0, total: 0, percentage: 0, abort: null };
+    }
+
+    const item = this.assets[key];
+    Object.assign(item, value);
+    item.percentage = Math.min(Math.floor((item.progress / item.total) * 100), 100);
+  }
+
+  add(key: string, total: number, abort?: AbortController) {
+    this.#update(key, { total, abort });
+  }
+
+  clear(key: string) {
+    this.#update(key, null);
+  }
+
+  update(key: string, progress: number, total?: number) {
+    const download: Partial<DownloadProgress> = { progress };
+    if (total !== undefined) {
+      download.total = total;
+    }
+    this.#update(key, download);
+  }
+}
+
+export const downloadStore = new DownloadStore();
+
+export const downloadManager = {
+  add: (key: string, total: number, abort?: AbortController) => downloadStore.add(key, total, abort),
+  clear: (key: string) => downloadStore.clear(key),
+  update: (key: string, progress: number, total?: number) => downloadStore.update(key, progress, total),
+};