feat: add downloadable release management for desktop client

- Extend DesktopClientReleaseCheckResponse with platform, arch, and channel fields.
- Introduce DesktopClientDownloadableRelease and DesktopClientDownloadableReleaseListResponse interfaces for managing downloadable releases.
- Implement ListDownloadable method in DesktopClientReleaseService to retrieve downloadable releases based on the specified channel.
- Update DesktopClientReleaseCheckResult to include platform, arch, and channel information.
- Add resolveInstallerDownloadURL method to handle download URL resolution for releases.
- Create new endpoint in DesktopReleaseHandler for listing downloadable releases.
- Update router to include the new downloadable releases route.
- Enhance tests to cover the new functionality for resolving download URLs and listing downloadable releases.

packages/shared-types/src/index.ts

@@ -145,6 +145,9 @@ export interface DesktopClientReleaseCheckResponse {
   update_available: boolean
   latest_version: string
   current_version: string
+  platform?: 'darwin' | 'win32' | 'linux' | string
+  arch?: 'universal' | 'x64' | 'arm64' | 'ia32' | string
+  channel?: string
   min_supported_version: string | null
   force_update: boolean
   download_source: 'oss' | 'custom'
@@ -164,10 +167,33 @@ export interface DesktopClientReleaseCheckResponse {
 }
 
 export interface DesktopClientReleaseDownloadURLResponse {
-  download_url: string
+  download_url?: string | null
   expires_in?: number | null
 }
 
+export interface DesktopClientDownloadableRelease {
+  id: number
+  platform: 'darwin' | 'win32' | 'linux' | string
+  arch: 'universal' | 'x64' | 'arm64' | 'ia32' | string
+  channel: string
+  version: string
+  download_url?: string | null
+  file_name?: string | null
+  file_size_bytes?: number | null
+  sha256?: string | null
+  release_notes?: string | null
+  published_at?: string | null
+  updated_at: string
+  force_update: boolean
+  min_supported_version?: string | null
+  download_source: 'oss' | 'custom' | string
+  oss_object_key?: string | null
+}
+
+export interface DesktopClientDownloadableReleaseListResponse {
+  items: DesktopClientDownloadableRelease[]
+}
+
 export type DesktopClientUpdateStage =
   | 'idle'
   | 'checking'