v0.2.3

Remove redundant mp3 intermediate conversion

• Local files (m4a/mp4/wav/etc): Skip mp3 step, convert directly to 16kHz WAV (~16s faster on long files)
• YouTube: Skip mp3 postprocessor in yt-dlp, keep native format (opus/webm) for direct WAV conversion — also avoids lossy mp3 re-encoding
• Output filenames: Remove _whisper suffix that was leaking from intermediate files into output markdown filenames