fix: vec4 vColor compatibility for three.js r183+

[sdivelbiss]

Summary

Closes #159

three.js r183 changed vColor from conditionally vec3/vec4 to always vec4 (three.js PR #32509). This causes GLSL shader compilation errors when using @three.ez/instanced-mesh:

ERROR: 0:506: '=' : dimension mismatch
ERROR: 0:506: 'assign' : cannot convert from 'const 3-component vector of float' to 'out highp 4-component vector of float'

Changes

• instanced_color_vertex.glsl: Always assign vec4 to vColor (removes USE_COLOR_ALPHA conditional)
• instanced_color_pars_vertex.glsl: Always return vec4 from getColorTexture() (removes vec3 branch)
• InstancedMesh2.ts: Always define USE_COLOR_ALPHA instead of conditionally setting USE_COLOR or USE_COLOR_ALPHA

Backward compatibility

This remains compatible with three.js r182 and earlier because USE_COLOR_ALPHA ensures vColor is declared as vec4 in older versions too. The colorsTexture is already created with 4 components (RGBA) and filled with 1.0, so the alpha channel is safely 1.0 by default when opacity is not used.

Repro

• Broken - https://jsfiddle.net/sdivelbiss/3urvnbhs/
• Fixed - https://jsfiddle.net/sdivelbiss/h3nbx01y/1/
• Backwards compatible with three@0.182.0 - https://jsfiddle.net/sdivelbiss/epmj8v5t/

Test plan

• Verified build succeeds with npm run build
• Verified no vec3(1.0) or bare vColor = color assignments in build output
• Tested rendering with three.js r183 in a real application — seats render correctly on foundations

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[agargaro]

Awesome, thank you! I'll test and merge it later :)

[agargaro]

Thanks! I've released a new version with the fix