feature: report the live player roster and kills from player management

[lukepolo]

Player Management now reports the live roster to the panel, so community servers get a live player list, session history and kill leaderboards.

• Every sync carries the verified players with a per-connection id, name, IP and kills/deaths, and any roster change triggers a debounced sync
• The roster is held through map changes and reloads, and an empty or hibernating server reports no players
• Departed players' final counters are kept until the panel confirms it recorded them
• Kills ignore bots, self-kills and teammates (unless teammates are enemies)