FIX UI nightfall

Features & Fixes 

1. EpicFight Nightfall Dedicated Server Crash Fix

• Problem: In NightFall (1.21.1), EffekUnits.VFXENABLE() and weapon animations try to access client-only configuration (EFNClientConfig) during entity ticking, causing immediate server shutdown whenever a player joins or executes combat animations.
• Solution: Uses SpongePowered Mixin (EffekUnitsMixin) to safely detect environment via FMLEnvironment.dist.isClient(). Dedicated servers safely bypass client visual configs while clients render 100% of particles, VFX, and animations smoothly.

2. Epic Fight: Skill Tree & Dodge Parry Reward GUI Crash Fix

• Problem: Opening the Skill Tree screen with custom skill addons (such as dodge_parry_reward) causes NullPointerException: Cannot invoke CategorySlotTexture.offsetX() because custom categories lack a hardcoded slot texture.
• Solution: Uses Mixin (NodeButtonMixin) to inject a safe fallback to CategorySlotTextures.PASSIVE whenever a custom category is encountered, allowing full functionality and rendering without crashes.

- Solution: Uses Mixin (`OpenGLExceptionMixin`) to intercept `checkGLError` and log non-fatal GL state warnings instead of terminating the client screen.