Fix merge job progress reporting showing 100% throughout

The -progress flag was being added AFTER the output path in the FFmpeg command,
causing FFmpeg to not recognize it and therefore not output progress information.

Moved -progress pipe:1 -nostats to appear BEFORE the output path.

Now merge jobs will correctly report progress as they encode:
- Progress starts at 0%
- Updates based on out_time_ms from FFmpeg progress output
- Calculates percentage based on total duration of all clips
- Shows accurate real-time progress in queue view and stats bar

main.go

@@ -2047,11 +2047,11 @@ func (s *appState) executeMergeJob(ctx context.Context, job *queue.Job, progress
 		}
 	}
 
-	args = append(args, outputPath)
-
-	// Add progress output for live updates
+	// Add progress output for live updates (must be before output path)
 	args = append(args, "-progress", "pipe:1", "-nostats")
 
+	args = append(args, outputPath)
+
 	// Execute
 	cmd := exec.CommandContext(ctx, platformConfig.FFmpegPath, args...)
 	utils.ApplyNoWindow(cmd)