feat(infra): add Jellyfin media server configuration and logging support

Add Jellyfin service to ansible inventory with hardware
transcoding and Casdoor SSO configuration. Configure
Alloy syslog listener to capture Jellyfin logs to Loki.
Update documentation with new service mapping and S3
bucket credential retrieval instructions.

ansible/jellyfin/jellyfin.service.j2

@@ -0,0 +1,18 @@
+---
+[Unit]
+Description=Jellyfin Docker Compose Service
+After=docker.service
+Requires=docker.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+WorkingDirectory={{ jellyfin_directory }}
+User={{ jellyfin_user }}
+ExecStart=/usr/bin/docker compose up -d
+ExecStop=/usr/bin/docker compose down
+Restart=on-failure
+RestartSec=30
+
+[Install]
+WantedBy=default.target