Add jellyfin stack, sharing plex's media library

Roku-accessible on the LAN via direct IP:8096; nginx proxy setup held
off for now. Reuses the existing nas_media volume and GPU passthrough
pattern from plex/docker-compose.yaml.

Claude-Session: https://claude.ai/code/session_01HZQK6jHmdTpFjFZM8FUnqA

jellyfin/docker-compose.yaml

@@ -0,0 +1,30 @@
+volumes:
+  nas_media:
+    external: true
+    name: nas_media
+services:
+  jellyfin:
+    container_name: jellyfin
+    image: jellyfin/jellyfin
+    restart: unless-stopped
+    ports:
+      - 8096:8096/tcp
+      - 8920:8920/tcp
+      - 7359:7359/udp
+    environment:
+      - TZ=America/New_York
+      - PUID=1000
+      - PGID=1000
+      - NVIDIA_VISIBLE_DEVICES=all
+      - NVIDIA_DRIVER_CAPABILITIES=compute,video,utility
+    volumes:
+      - /srv/jellyfin/config:/config
+      - /srv/jellyfin/cache:/cache
+      - nas_media:/data
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: all
+              capabilities: [gpu]