feat: switch to nvidia/cuda base image for NVENC hw encoding

- Base: nvidia/cuda:12.6.3-runtime-ubuntu24.04
- ffmpeg from apt has NVENC support when GPU runtime is available
- docker-compose reserves all GPUs via deploy.resources

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

docker-compose.yml

@@ -12,6 +12,13 @@ services:
       EXPORT_DIR: /exports
       DB_PATH: /data/8cut.db
       CACHE_DIR: /data/cache
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: all
+              capabilities: [gpu]
 
 volumes:
   8cut-data: