Add UIPlugin — embedded web UI for Fetcharr

[ParadauxIO]

Adds a new Maven module (UIPlugin) that serves a live web dashboard on port 8080 (configurable) using only the JDK's built-in HttpServer and pure HTML/CSS/JS with no external frontend dependencies.

How it works:

• Starts an embedded com.sun.net.httpserver.HttpServer on startup
• Subscribes to all FetcharrEvents and stores them in a capped circular buffer (default 500 entries)
• Serves a single-page dashboard at http://localhost:{port}/
• Pushes live updates to the browser via Server-Sent Events (/api/stream) with 25-second heartbeat keepalive to maintain the connection
• REST endpoints: /api/status (updaters + plugins JSON) and /api/events

UI features:

• Updaters panel — each *arr instance with type, URL, search amount, interval, missing status, monitored-only and cutoff flags
• Plugins panel — all loaded plugins with version and description
• Live activity log — newest-first, color-coded by service (Radarr=blue, Sonarr=green, Lidarr=orange, Whisparr=pink), with skipped/cancelled events visually dimmed
• Per-service filter buttons, full-text search, and clear log
• Dry Run badge in the header when fetcharr is in dry-run mode
• Status panel auto-refreshes every 15 seconds

This was vibecoded and used ~ 22,000 tokens
I hope it annoys reddit if you merge it