feat: add resumability detection and pause warnings

- Update 'fetch_metadata' to detect 'Accept-Ranges' HTTP header
- Persist 'resumable' flag in DownloadItem across backend and frontend
- Add confirmation dialog when pausing non-resumable downloads (single and bulk actions)
- Improve UI for start/pause/options buttons by adopting the application accent color on hover

src/utils/addDownloadMetadata.ts

@@ -27,6 +27,7 @@ export interface AddDownloadDraftRow {
   status: MetadataStatus;
   generation: number;
   isMedia: boolean;
+  resumable?: boolean;
   formats?: AddMediaFormat[];
   selectedFormat?: number;
 }