Player Damage Feedback

Initial release.

• Floating damage numbers for players. When a player takes damage, a number appears above them.
• Both sides see it. The victim sees the damage they took; if the hit came from another player, the attacker also sees the damage they dealt - shown in a different color by default.
• Server-authoritative, client-rendered. The server sends one packet to the victim and (if relevant) one to the attacker after LivingDamageEvent resolves, so the number always reflects real post-armor/enchantment damage. Each client renders independently and can turn its own view on/off without affecting anyone else.
• Configurable size, lifetime, rise speed, spread and colors via config/player_damage_feedback-client.toml. Size is a world-space scale factor, not pixels, since the numbers are 3D text billboards rendered in the world.