Adds six CRF vars, AUDIO_BITRATE, and three MONTAGE_* overlay durations.
Values match previous hardcoded defaults so behavior is unchanged.
The same CRF appeared in several scripts but with intentionally different
values per purpose (28 for draft intermediates, 26 for polished output).
Each script's CRF is now its own variable in conf, so changing one never
silently changes another.
https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ