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.ts

@@ -3,7 +3,7 @@
 // NO direct HTTP calls - everything routes through Rust backend
 
 import { commands } from "./bindings";
-import type { JRayActor } from "./bindings";
+import type { JRayActor, DownloadDiskUsage } from "./bindings";
 import type { QualityPreset } from "./quality-presets";
 import type {
   Library,
@@ -91,6 +91,31 @@ export class RepositoryClient {
     return commands.repositoryGetItem(this.ensureHandle(), itemId);
   }
 
+  /**
+   * Downloaded-only browse: libraries that contain downloaded content.
+   * Never merges server results; an empty list is authoritative.
+   * TRACES: UR-055 | DR-082
+   */
+  async getDownloadedLibraries(): Promise<Library[]> {
+    return commands.repositoryGetDownloadedLibraries(this.ensureHandle());
+  }
+
+  /**
+   * Downloaded-only browse: items under a container that are on the device.
+   * TRACES: UR-055 | DR-082, DR-083
+   */
+  async getDownloadedItems(parentId: string, options?: GetItemsOptions): Promise<SearchResult> {
+    return commands.repositoryGetDownloadedItems(this.ensureHandle(), parentId, options ?? null);
+  }
+
+  /**
+   * On-disk usage of downloaded content (device total + per-item/container bytes).
+   * TRACES: UR-056 | DR-085
+   */
+  async getDownloadDiskUsage(): Promise<DownloadDiskUsage> {
+    return commands.repositoryGetDownloadDiskUsage(this.ensureHandle());
+  }
+
   /**
    * Query the optional JRay plugin for the actors on screen at time `t`
    * (seconds) in an item. Resolves to an empty array when JRay isn't installed