[codex] Remove COORDINATE_SYSTEM.IDENTITY alias

[charlieforward9]

Goal

Remove the deprecated COORDINATE_SYSTEM.IDENTITY compatibility alias for the v10 cleanup.

Changes

• Removed the deprecated Object.defineProperty(COORDINATE_SYSTEM, 'IDENTITY', ...) getter and its warning-only log import.
• Replaced active test app and showcase usages with COORDINATE_SYSTEM.CARTESIAN.
• Removed unit-test coverage that only asserted the deprecated alias behavior.

Documentation

• Add this to the v10 What's New / release notes: COORDINATE_SYSTEM.IDENTITY has been removed; use COORDINATE_SYSTEM.CARTESIAN instead.

Validation

• yarn test-headless test/modules/core/shaderlib/project/project-functions.spec.ts test/modules/core/shaderlib/project/viewport-uniforms.spec.ts test/modules/mesh-layers/utils.spec.ts
• Pre-commit hook during commit: module/test/example lint and Prettier checks, lockfile validation, node Vitest smoke tests. Existing lint warnings were reported, with 0 errors.

[coveralls]

coverage: 83.389% (-0.002%) from 83.391% — codex/remove-coordinate-system-identity into master

[chrisgervang]

Let's hold on merging while we focus master on 9.4 betas