Restructure audio into AUDIO_DIR with per-camera retention

New AUDIO_DIR variable (like BASE_DIR/MOVIES_DIR) is the root for all
audio recordings.  Set in .env to put audio on a separate drive.

Directory layout:
  AUDIO_DIR/<cam>/YYYY-MM-DD/HH-MM-SS.m4a        — ambient recordings
  AUDIO_DIR/sunrise/<cam>/YYYY-MM-DD/sunrise-audio.m4a — sunrise clips

sky-cam.conf:
- Add AUDIO_DIR="${AUDIO_DIR:-$BASE_DIR/audio}" in storage section
- Remove AMBIENT_DIR (replaced by AUDIO_DIR)
- Add SUNRISE_AUDIO_RETENTION_DAYS=7 (sunrise clips kept separately from ambient)
- Add per-camera ambient retention examples:
    AMBIENT_RETENTION_DAYS_south=60  (keep bird recordings longer)

ambient-record.sh:
- Use AUDIO_DIR instead of AMBIENT_DIR
- Per-camera retention: AMBIENT_RETENTION_DAYS_<cam> overrides global default

sunrise-audio-capture.sh:
- Save clips to AUDIO_DIR/sunrise/<cam>/<date>/sunrise-audio.m4a
- Rolling retention of sunrise clips (SUNRISE_AUDIO_RETENTION_DAYS)

daily_sunrise_video.sh:
- Look for cam_audio in new AUDIO_DIR/sunrise path first, fall back to
  old BASE_DIR path so existing recordings keep working

install.sh:
- Pre-create AUDIO_DIR/<cam> and AUDIO_DIR/sunrise/<SUNRISE_CAM> dirs
- Add AUDIO_DIR to .env.example storage section

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

install.sh

@@ -37,10 +37,13 @@ echo "Creating data directories..."
 for cam in "${CAMERAS[@]}"; do
     mkdir -p "$BASE_DIR/$cam"
     mkdir -p "$MOVIES_DIR/$cam"
+    mkdir -p "$AUDIO_DIR/$cam"
     echo "  $BASE_DIR/$cam"
     echo "  $MOVIES_DIR/$cam"
+    echo "  $AUDIO_DIR/$cam"
 done
 mkdir -p "$BASE_DIR/$SUNRISE_CAM"
+mkdir -p "$AUDIO_DIR/sunrise/$SUNRISE_CAM"
 echo ""
 
 # ── Helper: write a oneshot service unit ─────────────────────────────────────
@@ -262,6 +265,7 @@ env_example="$HERE/.env.example"
     echo "# different drive.  Leave commented to use the defaults next to the scripts."
     echo "#BASE_DIR=/path/to/images          # default: ~/sky-cam/data"
     echo "#MOVIES_DIR=/path/to/videos        # default: \$BASE_DIR/movies"
+    echo "#AUDIO_DIR=/path/to/audio          # default: \$BASE_DIR/audio"
     echo "#MUSIC_DIR=/path/to/music/4Seasons # default: ~/sky-cam/music"
     echo ""
     echo "# ── RTSP stream URLs ────────────────────────────────────────────────────────"