scripts: rewrite append_signals.py for linescan scrolling video

Complete rewrite to properly handle linescan image sequences:
- Stitches linescan images horizontally into wide panorama
- Creates scrolling video that pans left-to-right
- Configurable scroll speed based on capture rate (750 lines/sec)
- Output saved one folder up from image source
- Uses Pillow for image stitching, ffmpeg for video creation

Features:
- --scroll-speed: multiplier for playback speed (1.0 = real-time)
- --lines-per-second: linescan capture rate (default: 750)
- --max-frames: limit frames for testing
- --fps: output video framerate (default: 30)
- --width: viewport width (default: 1920)
- Automatic cleanup of temporary stitched image

Example usage:
  # Real-time playback
  uv run scripts\append_signals.py results\20251122\bumpy-filter

  # 2x speed
  uv run scripts\append_signals.py results\20251122\bumpy-filter --scroll-speed 2.0

  # Test with 10 frames
  uv run scripts\append_signals.py results\20251122\bumpy-filter --max-frames 10

scripts/append_signals.py

@@ -7,8 +7,11 @@
 # ///
 
 """
-Stitch linescan frame sequences horizontally and create scrolling video.
-Linescan images are concatenated side-by-side and played as a scrolling video.
+Create scrolling panorama videos from linescan image sequences.
+
+This script stitches linescan images horizontally into a wide panorama,
+then creates a scrolling video that pans left-to-right across the stitched image.
+The scroll speed is calibrated to the linescan capture rate (750 lines/second by default).
 """
 
 import argparse