Mediumcore Fix

Fixes health data loss when updating Alex's Mediumcore mod

Problem

The original Mediumcore in onLivingDeath uses player.getMaxHealth(), which INCLUDES modifiers from external sources (rings, armor, etc.).

Example with a +20 HP ring:

• maxHealth = 40 (20 base + 20 ring)
• clippedHealth = clip(40 - 2, 6, 20) = 20 (clamped to maxPlayerHealth!)
• healthModifiedBy = 0 + (20 - 40) = -20!
• After respawn: maxHealth = 20 + 0 + (-20) = 0 HP → the player gains 1 HP.

Solution

Introduce BASE_HEALTH_TAG to store the "pure" base health, which is independent of external modifiers.