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

4-seasons.sh

@@ -72,6 +72,10 @@ if [ "$total_images" -lt 1 ]; then
 fi
 echo "Images found: $total_images"
 
+# ── Per-camera capture interval ───────────────────────────────────────────────
+interval_var="CAPTURE_INTERVAL_${CAM_NAME}"
+INTERVAL="${!interval_var:-${CAPTURE_INTERVAL:-10}}"
+
 # ── Prepare output directory ──────────────────────────────────────────────────
 output_dir="$MOVIES_DIR/$CAM_NAME/$ASTRO_YEAR/$SEASON/Mvt$MVT_NUM"
 mkdir -p "$output_dir"
@@ -82,12 +86,14 @@ temp_video="$output_dir/${yesterday}_Mvt${MVT_NUM}-temp.mp4"
 cleanup() { rm -f "$temp_file" "$temp_video" 2>/dev/null || true; }
 trap cleanup EXIT
 
-find "$image_dir" -type f -name "*.jpg" | sort | while read -r img; do
-    echo "file '$img'"
+mapfile -t images < <(find "$image_dir" -type f -name "*.jpg" | sort)
+for img in "${images[@]}"; do
+    printf "file '%s'\nduration %s\n" "$img" "$INTERVAL"
 done > "$temp_file"
+printf "file '%s'\n" "${images[-1]}" >> "$temp_file"
 
-# ── Step 1: Build raw video at default frame rate ─────────────────────────────
-echo "Step 1/2: encoding raw video..."
+# ── Step 1: Build raw video ───────────────────────────────────────────────────
+echo "Step 1/2: encoding raw video from ${#images[@]} frames..."
 ffmpeg -loglevel warning \
     -f concat -safe 0 -i "$temp_file" \
     -c:v libx264 -pix_fmt yuv420p -preset "$ENCODE_PRESET" -crf "$CRF_SEASONS_RAW" -vsync 2 -an \
@@ -103,7 +109,7 @@ echo "Step 2/2: speed factor $speed_factor..."
 final_file="$output_dir/${yesterday}_Mvt${MVT_NUM}-Day${DAY_OF_MVT}of${DAYS_IN_MVT}-final.mp4"
 if ! ffmpeg -loglevel warning \
     -i "$temp_video" \
-    -vf "setpts=PTS/$speed_factor" \
+    -vf "setpts=PTS/$speed_factor,fps=25" \
     -c:v libx264 -pix_fmt yuv420p -preset "$ENCODE_PRESET" -crf "$CRF_SEASONS_FINAL" \
     -t "$target_per_clip" -an \
     -y "$final_file"; then