feat(seedbox): add Transmission stack with Tailscale sidecar

- WebUI accessible via transmission.taila5ad8.ts.net (HTTPS)
- Peer port 51413 exposed publicly for seeding
- Local downloads + NFS media mount

seedbox/stacks/transmission/docker-compose.yml

@@ -0,0 +1,45 @@
+services:
+  ts-transmission:
+    image: tailscale/tailscale:latest
+    hostname: transmission
+    environment:
+      - TS_AUTHKEY=${TS_AUTHKEY}
+      - TS_EXTRA_ARGS=--advertise-tags=tag:container
+      - TS_STATE_DIR=/var/lib/tailscale
+      - TS_SERVE_CONFIG=/config/serve.json
+      - TS_USERSPACE=false
+    volumes:
+      - ts-state:/var/lib/tailscale
+      - ./serve.json:/config/serve.json:ro
+    devices:
+      - /dev/net/tun:/dev/net/tun
+    cap_add:
+      - net_admin
+    ports:
+      # BitTorrent peer port - exposed publicly for seeding
+      - "51413:51413"
+      - "51413:51413/udp"
+    restart: unless-stopped
+
+  transmission:
+    image: linuxserver/transmission:latest
+    container_name: transmission
+    network_mode: service:ts-transmission
+    depends_on:
+      - ts-transmission
+    environment:
+      - PUID=1000
+      - PGID=1000
+      - TZ=Europe/Paris
+      - USER=${TRANSMISSION_USER:-admin}
+      - PASS=${TRANSMISSION_PASS}
+      - PEERPORT=51413
+    volumes:
+      - config:/config
+      - /srv/seedbox/downloads:/downloads
+      - /mnt/media:/media
+    restart: unless-stopped
+
+volumes:
+  ts-state:
+  config: