feat: Add 8 new custom API widgets (TrueNAS, Jellyfin, Radarr, Sonarr, Plex, Cloudflare, Tailscale, Netbird)

[kirolos-esmat]

This PR introduces 8 new custom API widgets for monitoring the following services:

1. TrueNAS Metrics - System load average, live uptime, active TrueNAS alerts counter, and CPU model
2. Jellyfin Stats - Live active playback streams (with dynamic highlight when sessions are active) and total movies & series counts
3. Radarr Stats - Total movie library count, missing movies, and active download queue
4. Sonarr Stats - Total series library count, missing episodes, and active download queue
5. Plex Stats - Native Plex API active sessions (dynamic highlight), active streams list by user/title, and library movie/show counts
6. Cloudflare Tunnel Status - Cloudflare connector tunnel live health status and origin IP
7. Tailscale Device Status - Live IP address, relative last seen timestamp, and key expiry for a specific Tailscale device
8. Netbird Peers Count - Real-time total connected network peer count for your Netbird network

All widgets use environment variables for API keys and URLs where appropriate, and include preview screenshots and required meta.yml files.