feat(downloads): browsable downloaded library with on-disk usage

Replace the flat download list with a Downloaded browse surface that
reuses the online grids/cards/detail pages, filtered to on-device media,
plus a demoted Transfers tab. Add repository browse commands
(getDownloadedLibraries/Items, disk usage) with offline/hybrid
implementations, a downloadedCatalog service, formatBytes helper, and
per-item/device disk-usage labels on cards and grids. Regenerated
bindings.

Also carries the inseparable UR-052 offline-filter hunks in
offline.rs/hybrid.rs.

TRACES: UR-055 | DR-081, DR-082, DR-083, DR-084; UR-056 | DR-085

src/lib/api/repository-client.test.ts

@@ -337,6 +337,46 @@ describe("RepositoryClient", () => {
         requestId: 0,
       });
     });
+
+    // Downloaded-only browse path (UR-055 | DR-082) — verifies command names and
+    // camelCase params per the Tauri v2 rule (CLAUDE.md).
+    it("should get downloaded libraries from backend", async () => {
+      const mockLibraries = [{ id: "lib1", name: "Music", collectionType: "music" }];
+      (invoke as any).mockResolvedValueOnce(mockLibraries);
+
+      const libraries = await client.getDownloadedLibraries();
+
+      expect(libraries).toEqual(mockLibraries);
+      expect(invoke).toHaveBeenCalledWith("repository_get_downloaded_libraries", {
+        handle: "test-handle-123",
+      });
+    });
+
+    it("should get downloaded items with camelCase params", async () => {
+      const mockResult = { items: [{ id: "t1", name: "Track", type: "Audio" }], totalRecordCount: 1 };
+      (invoke as any).mockResolvedValueOnce(mockResult);
+
+      const result = await client.getDownloadedItems("album1", { limit: 50 });
+
+      expect(result).toEqual(mockResult);
+      expect(invoke).toHaveBeenCalledWith("repository_get_downloaded_items", {
+        handle: "test-handle-123",
+        parentId: "album1",
+        options: { limit: 50 },
+      });
+    });
+
+    it("should get download disk usage from backend", async () => {
+      const mockUsage = { sizes: { t1: 1000 }, partialContainers: {}, deviceTotalBytes: 1000, itemCount: 1 };
+      (invoke as any).mockResolvedValueOnce(mockUsage);
+
+      const usage = await client.getDownloadDiskUsage();
+
+      expect(usage).toEqual(mockUsage);
+      expect(invoke).toHaveBeenCalledWith("repository_get_download_disk_usage", {
+        handle: "test-handle-123",
+      });
+    });
   });
 
   describe("Playback Methods", () => {