Filler-word removal

Goal: cut filler words so the result sounds natural — no clipped consonants, no abrupt audio jumps, no real speech lost. This is an iterative process; do not stop at the first pass.

Step 0 (CRITICAL): get a verbatim transcript

mlx-whisper silently cleans disfluencies by default — it drops most "um/uh" from the transcript, so there's nothing to cut. This was the root cause of a past failure where fillers survived the edit.

transcribe is now verbatim by default: it seeds the decoder with a short hesitation prompt (Um, uh, er, hmm...) and condition_on_previous_text=False, so um/uh are kept. Just run:

uv run video-agent transcribe video.mp4 --words -o words.txt   # start_sec  end_sec  word