Transmission #025: Stylized3DMonster material shader references fixed

The cel-shaded monster materials under Assets/Stylized3DMonster/ all pointed at a shader GUID that does not exist in this project (b1d48c9879e633847a7c4a35365adbd8), so Unity showed Hidden/InternalErrorShader on those materials. Each PixeliusVita pack ships its own copy of MonsterCelShaderOption.shader with a different .meta GUID per folder.

Materials were updated so each monster pack’s .mat files reference that pack’s ShaderMaster/MonsterCelShaderOption.shader GUID (Monster02–Monster06). This matches the intent of Documentation.txt (URP + the included cel shaders); the broken state was a missing shader reference, not an extra manual setup step beyond URP.

After reimport or opening the project, the materials should resolve to Custom/Flat2D_Outline_Rim_Metallic_Emission_Opaque and compile normally.