Add pure-ffmpeg RTSP capture and camera audio for sunrise videos

Removes dependency on MotionEye or any NVR software.  Everything is now
CLI/ffmpeg configured entirely from sky-cam.conf.

capture.sh
  Long-running systemd service (one per camera) that pulls frames from the
  camera's RTSP stream at CAPTURE_INTERVAL seconds, writing HH-MM-SS.jpg
  into BASE_DIR/<cam>/YYYY-MM-DD/.  Restarts at midnight for the new date
  directory; auto-reconnects on camera disconnect.

sunrise-audio-capture.sh
  One-shot service triggered at 03:00.  Waits until (sunrise minus
  SUNRISE_PRE_MIN minus AUDIO_PRE_BUFFER_MIN), then records the RTSP audio
  stream for the full sunrise window.  Output deleted after mixing.

daily_sunrise_video.sh
  Step 3 now mixes in sunrise-audio.m4a when AUDIO_ENABLED=true and the
  file exists.  Audio is centred on actual sunrise time at natural speed
  while the video plays as the sped-up timelapse.  Uses filter_complex
  when audio is present (can't combine -vf with -filter_complex).

install.sh
  Generates sky-cam-capture-<cam>.service for each camera with CAM_RTSP_<cam>
  set, and sky-cam-audio-capture.{service,timer} when AUDIO_ENABLED=true.

sky-cam.conf
  New settings: CAM_RTSP_<cam>, CAPTURE_INTERVAL, AUDIO_ENABLED,
  AUDIO_PRE_BUFFER_MIN, CAPTURE_AUDIO_BITRATE.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

daily_sunrise_video.sh

@@ -139,19 +139,41 @@ DT="${DT}:line_spacing=4"
 DT="${DT}:x=w-tw-18:y=(h-th)/2"
 DT="${DT}:shadowcolor=black@0.55:shadowx=1:shadowy=1"
 
-# ── Step 3: Overlay — sunrise time burned in ──────────────────────────────────
-# If overlay fails, the sped video is promoted to the upload target so
-# OnSuccess still fires and the upload happens (without timestamp overlay).
+# ── Step 3: Overlay + optional audio ─────────────────────────────────────────
+# With audio: DT must go into -filter_complex (can't mix -vf and -filter_complex)
+# Without audio: plain -vf is simpler and avoids any filter_complex overhead.
+# If overlay fails either way, the sped video is promoted so upload still fires.
 final_video="$output_dir/$current_date-daily-sunrise.mp4"
-echo "Step 3/3: overlay → $final_video"
-if ffmpeg -loglevel warning \
-    -i "$sped_video" \
-    -vf "${DT}" \
-    -c:v libx264 -pix_fmt yuv420p -crf "$CRF_SUNRISE" -an \
-    -y "$final_video"; then
+audio_file="$image_dir/sunrise-audio.m4a"
+step3_ok=true
+
+if [ "${AUDIO_ENABLED:-false}" = "true" ] && [ -f "$audio_file" ]; then
+    buffer_sec=$(( ${AUDIO_PRE_BUFFER_MIN:-2} * 60 ))
+    audio_offset=$(echo "scale=1; $SUNRISE_PRE_MIN * 60 + $buffer_sec - $SUNRISE_TARGET_SECS / 2" | bc)
+    fade_out=$(echo "scale=1; $SUNRISE_TARGET_SECS - 0.5" | bc)
+    echo "Step 3/3: overlay + camera audio (offset ${audio_offset}s) → $final_video"
+    ffmpeg -loglevel warning \
+        -i "$sped_video" \
+        -ss "$audio_offset" -t "$SUNRISE_TARGET_SECS" -i "$audio_file" \
+        -filter_complex "[0:v]${DT}[vout];[1:a]afade=t=in:st=0:d=0.5,afade=t=out:st=${fade_out}:d=0.5[aout]" \
+        -map "[vout]" -map "[aout]" \
+        -c:v libx264 -pix_fmt yuv420p -crf "$CRF_SUNRISE" \
+        -c:a aac -b:a 128k \
+        -y "$final_video" || step3_ok=false
+else
+    echo "Step 3/3: overlay (no audio) → $final_video"
+    ffmpeg -loglevel warning \
+        -i "$sped_video" \
+        -vf "${DT}" \
+        -c:v libx264 -pix_fmt yuv420p -crf "$CRF_SUNRISE" -an \
+        -y "$final_video" || step3_ok=false
+fi
+
+if $step3_ok; then
     actual_dur=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$final_video")
     echo "Done: $final_video  (${actual_dur}s, sunrise at ${SR_TIME})"
     rm -f "$sped_video"
+    [ -f "$audio_file" ] && rm -f "$audio_file"
     "$SCRIPT_DIR/notify.sh" "Sunrise ready: $current_date" \
         "$(basename "$final_video") — ${actual_dur}s, sunrise at ${SR_TIME}" || true
 else