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/downloadFailure.ts

@@ -18,3 +18,10 @@ export function failCopyKeys(
     ...(code === "unknown" ? [] : [category("unknown")]),
   ];
 }
+
+/** The title over a failed job's explanation: an upload's failure is a conversion, not a download. */
+export function failTitleKey(job: Pick<DownloadJob, "job_kind">): string {
+  return job.job_kind === "upload"
+    ? "downloads.errors.fail.titleUpload"
+    : "downloads.errors.fail.title";
+}