fix: progress always at 0% and context cancelled before sendDocument

- Fix progress template: remove spurious stderr: prefix and switch to
  _percent_str/_speed_str/_eta_str keys (progress.percent outputs NA
  for HLS streams with unknown total size)
- Update progress regex to match new template format:
  DLPROG| 45.2%|   1.05MiB/s|00:45
- Fix context cancellation bug: clearActiveJob was cancelling dlCtx
  before handleDownloadCompletion could send the document
- Update progress test cases to match new template output format

internal/dl/ytdlp.go

@@ -285,7 +285,7 @@ func (c *Client) StartDownload(job *domain.DownloadJob, downloadDir string) (<-c
 
 	// Progress reporting using progress-template for machine-readable output
 	args = append(args, "--newline")
-	args = append(args, "--progress-template", "stderr:DLPROG|%(progress.percent)s|%(progress.speed)s|%(progress.eta)s")
+	args = append(args, "--progress-template", "DLPROG|%(progress._percent_str)s|%(progress._speed_str)s|%(progress._eta_str)s")
 
 	// Language selection if specified
 	if job.Language != "" {