Color grade (LUTs via ffmpeg)

Grade through LUT files rather than re-deriving filter params each time. Two LUT formats, both native to ffmpeg, no extra deps:

• .cube — a 3D LUT (what colorists ship). Applied with lut3d.
• .png HALD-CLUT — a look baked from a filter chain (below). Applied with haldclut.

The grade command auto-detects by extension.

# Apply a look
uv run video-agent grade apply in.mp4 --lut luts/teal_orange.cube -o out.mp4
uv run video-agent grade apply in.mp4 --lut luts/warm.png        -o out.mp4   # HALD

"Make a few looks and let me choose"

The best grading UX: render the SAME frame through several candidate looks into one labelled contact sheet, show it, let the user pick — then apply the winner to the whole video.