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

sky-cam.conf

@@ -150,6 +150,9 @@ SCRIPT_DIR="${SCRIPT_DIR:-$(dirname "$(realpath "${BASH_SOURCE[0]}")")}"
 BASE_DIR="${BASE_DIR:-$SCRIPT_DIR/data}"
 MOVIES_DIR="${MOVIES_DIR:-$BASE_DIR/movies}"  # override if videos live on a different drive
 MUSIC_DIR="${MUSIC_DIR:-$SCRIPT_DIR/music}"
+AUDIO_DIR="${AUDIO_DIR:-$BASE_DIR/audio}"     # root for all audio recordings; override in .env
+#   Structure: AUDIO_DIR/<cam>/YYYY-MM-DD/HH-MM-SS.m4a         (ambient)
+#              AUDIO_DIR/sunrise/<cam>/YYYY-MM-DD/sunrise-audio.m4a  (sunrise clips)
 
 # ── Location & timezone ───────────────────────────────────────────────────────
 # Used by sunrise.py to calculate sunrise time each day.
@@ -321,6 +324,9 @@ AUDIO_ENABLED=false           # set true if your camera has a working mic
 CAPTURE_AUDIO_BITRATE=96k     # bitrate for the sunrise audio recording
 # Audio is recorded for exactly SUNRISE_TARGET_SECS, centred on actual sunrise:
 # floor(TARGET/2) seconds before, ceil(TARGET/2) after (odd second → post-sunrise).
+# Clips are saved to AUDIO_DIR/sunrise/<cam>/YYYY-MM-DD/sunrise-audio.m4a.
+# After mixing into the video the clip is kept for SUNRISE_AUDIO_RETENTION_DAYS, then deleted.
+SUNRISE_AUDIO_RETENTION_DAYS=7
 
 # ── Ambient audio library ──────────────────────────────────────────────────────
 # Continuously records natural sounds (birds, rain, wind) from AMBIENT_CAMS to
@@ -330,10 +336,14 @@ CAPTURE_AUDIO_BITRATE=96k     # bitrate for the sunrise audio recording
 #
 AMBIENT_ENABLED=false
 AMBIENT_CAMS=(south)                    # cameras to record from
-AMBIENT_DIR="${BASE_DIR}/ambient"       # root storage directory
 AMBIENT_CHUNK_SECS=1800                 # seconds per file (default 30 min)
 AMBIENT_BITRATE=96k                     # AAC bitrate; 64–96k is plenty at 8 kHz
-AMBIENT_RETENTION_DAYS=30              # delete files older than this; 0 = keep forever
+# Retention — global default, then optional per-camera overrides.
+# Uncomment and set per-cam lines to keep different cameras for different durations.
+AMBIENT_RETENTION_DAYS=30              # global default; 0 = keep forever
+#AMBIENT_RETENTION_DAYS_east=14
+#AMBIENT_RETENTION_DAYS_north=30
+#AMBIENT_RETENTION_DAYS_south=60       # keep south longer for nature sound library
 
 # ── Mattermost — daily sunrise upload ─────────────────────────────────────────
 # mattermost_url, access_token, channel_id go in .env (see bottom of this file).