Add HDR OpenEXR cube face export

[andy83]

Summary

• export the existing HDR cube render target directly as six OpenEXR files
• add a Cube faces EXR (.zip) option to normal, batch, per-layer, and composite exports
• preserve all existing PNG and equirectangular HDR/EXR export paths and canonical face naming

Implementation

BinaryConstruct already bakes its cubemap into a HalfFloatType render target. The new path reads each face into a Uint16Array, wraps that half-float data in a Three.js DataTexture, and encodes it with Three.js' EXRExporter. No 8-bit PNG or other LDR intermediate is involved.

Faces are read and encoded sequentially so the 4096×4096 export does not retain six additional uncompressed conversion buffers at once.

Verification

• npm test: 17 files, 135 tests passed
• npm run build: passed
• npm run lint: passed with the repository's existing react(only-export-components) warning in src/ui/SpritesTab.tsx
• browser verification with real presets and HDR multipliers above 1.0
• all six 4096×4096 EXRs verified as half-float with HDR values above 1.0
• PNG/EXR face orientation compared pixel-for-pixel across all six faces
• repeated EXR exports verified byte-identical per archive entry
• batch and per-layer/composite EXR packaging verified