Add MOVIES_DIR to conf; remove hardcoded 'movies' subdir

All scripts now use $MOVIES_DIR instead of $BASE_DIR/movies.
Defaults to BASE_DIR/movies but can point to a separate drive.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

year-end-join.sh

@@ -8,7 +8,7 @@
 # The 12 individual movement videos already carry their own attribution overlay
 # (first 6 seconds of each), so no extra card is appended here.
 #
-# Output: $BASE_DIR/movies/$CAM_NAME/$ASTRO_YEAR/$CAM_NAME-$ASTRO_YEAR.mp4
+# Output: $MOVIES_DIR/$CAM_NAME/$ASTRO_YEAR/$CAM_NAME-$ASTRO_YEAR.mp4
 
 set -euo pipefail
 
@@ -23,7 +23,7 @@ fi
 # Camera name: second argument overrides conf (passed through from montage-mvt.sh).
 CAM_NAME="${2:-$CAM_NAME}"
 
-year_dir="$BASE_DIR/movies/$CAM_NAME/$ASTRO_YEAR"
+year_dir="$MOVIES_DIR/$CAM_NAME/$ASTRO_YEAR"
 
 echo "Assembling Four Seasons $ASTRO_YEAR from $year_dir ..."