Expose encoding quality and overlay durations in sky-cam.conf

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

fullday-video.sh

@@ -63,7 +63,7 @@ echo "Creating: $output_file"
 
 ffmpeg -loglevel warning \
     -f concat -safe 0 -i "$temp_list" \
-    -c:v libx264 -pix_fmt yuv420p -crf 28 \
+    -c:v libx264 -pix_fmt yuv420p -crf "$CRF_FULLDAY" \
     -an -y "$output_file"
 
 actual_dur=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$output_file")