fix(downloads): an upload's cancel, progress, failure and notice speak of an upload

- Cancelling an upload asks "Delete upload?" and says the uploaded file is
  removed from the server with it.
- The phone-safe conversion's real ffmpeg % shows as a bar ("Converting for
  phones"), not an indeterminate pulse.
- A failed upload is titled "The upload isn't ready", with its own reasons
  (convert_failed, retryable; upload_missing) instead of download copy.
- The inbox says "Upload ready to share" for a converted upload.

frontend/src/lib/api/downloads.ts

@@ -89,7 +89,7 @@ export interface DownloadJob {
   display_uploader: string | null; // user override of the channel name
   display_uploader_url: string | null; // user override of the channel link
   extra_links: string[]; // extra reference URLs (beyond source_url)
-  job_kind?: DownloadJobKind; // "download" (default) | "edit" (a per-user trim/crop derivative)
+  job_kind?: DownloadJobKind; // see DownloadJobKind; absent reads as "download"
   source_job_id?: number | null; // parent download an edit was cut from
   edit_spec?: EditSpec | null;
   can_download: boolean;