Prepend <cam> to all output filenames consistently

Audio:
  AUDIO_DIR/<cam>/YYYY-MM-DD/<cam>-HH-MM-SS.m4a

Movies — cam name now always leads the filename:
  daily_sunrise_video.sh:
    east-2026-04-22-daily-sunrise.mp4
    east-2026-04-22-daily-sunrise-sped.mp4  (intermediate)
    east-2026-04-22-daily-sunrise-test.mp4  (demo)
  4-seasons.sh:
    east-2026-04-21_Mvt2-Day2of31-final.mp4  (was: 2026-04-21_east_Mvt2-...)
  montage-mvt.sh:
    east-2026-03-20_Spring_Mvt1-Sped.mp4
    east-2026-03-20_Spring_Mvt1-Montage.mp4
  year-end-join.sh:
    east-2026.mp4  (already had cam at front)

sunrise2mm.py updated to look for the new east-YYYY-MM-DD-daily-sunrise.mp4
filename. Retention find patterns (wildcards) already match both formats.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

montage-mvt.sh

@@ -147,7 +147,7 @@ concat_dur=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$temp_c
 speed_factor=$(echo "scale=6; $concat_dur / $effective_duration" | bc)
 echo "Step 2/3: speed $speed_factor  (raw=${concat_dur}s → target=${effective_duration}s)"
 
-sped_file="$output_dir/${MVT_START}_${SEASON}_Mvt${MVT_NUM}-Sped.mp4"
+sped_file="$output_dir/${CAM_NAME}-${MVT_START}_${SEASON}_Mvt${MVT_NUM}-Sped.mp4"
 if ! ffmpeg -loglevel warning \
     -i "$temp_concat" \
     -vf "setpts=PTS/$speed_factor" \
@@ -193,7 +193,7 @@ DT="${DT}:fontcolor=0xCCCCCC:fontsize=h/36:x=(w-text_w)/2:y=h*0.113"
 DT="${DT}:box=1:boxcolor=black@0.55:boxborderw=5"
 DT="${DT}:alpha='${ALPHA}':enable='${ENABLE}'"
 
-output_file="$output_dir/${MVT_START}_${SEASON}_Mvt${MVT_NUM}-Montage.mp4"
+output_file="$output_dir/${CAM_NAME}-${MVT_START}_${SEASON}_Mvt${MVT_NUM}-Montage.mp4"
 
 # If music/overlay fails, the sped video is promoted to the output path so
 # year-end-join can still include this movement (as a silent, no-overlay clip).