Per-camera capture interval; ambient recorder; fix 4-seasons one-frame bug

Per-camera capture interval:
  CAPTURE_INTERVAL_<cam> in sky-cam.conf overrides the global value for
  a specific camera.  capture.sh and 4-seasons.sh both respect it.
  Example: south at 30s saves storage; north at 5s gives smoother motion.

4-seasons.sh one-frame bug fix:
  Same root cause as the sunrise scripts — concat list had no 'duration'
  entries, collapsing all JPEG frames to timestamp 0.  Fixed by writing
  'duration INTERVAL' per frame.  Added fps=25 to the speed-adjust step
  so the VFR source resamples to a standard frame rate.

ambient-record.sh (new):
  Continuous AAC recorder for natural sounds (birds, rain, wind).
  Saves AMBIENT_CHUNK_SECS chunks to AMBIENT_DIR/<cam>/YYYY-MM-DD/HH-MM-SS.m4a.
  Reconnects automatically on stream failure.  Rolling retention via
  AMBIENT_RETENTION_DAYS.  Enabled by setting AMBIENT_ENABLED=true and
  listing cameras in AMBIENT_CAMS in sky-cam.conf, then re-running install.sh.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

install.sh

@@ -187,6 +187,38 @@ if [ "${AUDIO_ENABLED:-false}" = "true" ]; then
     timers+=("sky-cam-audio-capture")
 fi
 
+# ── Ambient audio recording services ─────────────────────────────────────────
+# One long-running service per camera in AMBIENT_CAMS.
+# Enabled alongside the capture services so install.sh restarts them on update.
+if [ "${AMBIENT_ENABLED:-false}" = "true" ]; then
+    for cam in "${AMBIENT_CAMS[@]}"; do
+        rtsp_var="CAM_RTSP_${cam}"
+        if [ -n "${!rtsp_var:-}" ]; then
+            cat > "$UNIT_DIR/sky-cam-ambient-${cam}.service" <<EOF
+[Unit]
+Description=Sky-Cam — ${cam}: ambient audio recorder
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=$SCRIPT_DIR/ambient-record.sh ${cam}
+Restart=on-failure
+RestartSec=30
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=default.target
+EOF
+            echo "  wrote sky-cam-ambient-${cam}.service"
+            capture_services+=("sky-cam-ambient-${cam}")
+        else
+            echo "  WARNING: CAM_RTSP_${cam} not set — skipping ambient service for ${cam}"
+        fi
+    done
+fi
+
 # ── Per-camera Four Seasons jobs ─────────────────────────────────────────────
 # Reads CAMERAS and SCHEDULE_SEASONS_<cam> from sky-cam.conf.
 # Script receives the camera name as $1 so it knows which camera to process.