fix: add libonig-dev for mbstring; update scanner for data discs

Dockerfile: add libonig-dev (oniguruma) — required by mbstring extension

scanner/scan_disc.py:
- Treat all discs as data discs (mp4/mkv/etc), no VIDEO_TS/BDMV logic
- List video files by extension (.mp4 .mkv .avi .mov .m4v .ts .m2ts …)
- Infer media type from drutil type string, fall back to used_gb capacity
  (>8 GB → Blu-ray, >0.68 GB → DVD, smaller → CD)
- Store video file names in comment field, count in custom2

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

videodb/Dockerfile

@@ -5,6 +5,7 @@ RUN apt-get update && apt-get install -y \
     libpng-dev \
     libjpeg-dev \
     libfreetype6-dev \
+    libonig-dev \
     default-mysql-client \
     && rm -rf /var/lib/apt/lists/*