Add initial SOG format support

[querielo]

Issue: #476

This PR adds first-class support for the SOG (Spatially Ordered Gaussians) scene format to GaussianSplats3D. It enables loading both:

• A bundled .sog archive (ZIP with stored entries), and
• A multi-file SOG directory containing meta.json and referenced WebP images.

Limitations and follow-ups

• Zip reader supports only STORE (no DEFLATE). This matches the splat-transform writer.
• SH degree 3 data is currently clamped to degree 2. Follow-up: import all 15 AC coefficients per channel when viewer-side support is in place.
• Consider workerizing SOG parsing for large scenes to keep the main thread responsive.

[Copilot]

Pull Request Overview

This PR adds initial support for the SOG (Spatially Ordered Gaussians) scene format to GaussianSplats3D, enabling loading of both bundled .sog archives and multi-file SOG directories.

Key changes include:

• Implementation of a minimal ZIP reader for browser-based .sog archive extraction (STORE method only)
• SOG parser that reconstructs 3D Gaussian splats from WebP-encoded data using quantization and codebooks
• Integration with existing loader infrastructure and viewer components

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/loaders/sog/ZipReaderBrowser.js	Minimal ZIP reader supporting STORE compression for .sog archives
src/loaders/sog/SogParser.js	Core parser for SOG format data reconstruction from WebP images
src/loaders/sog/SogLoader.js	Main loader with support for both directory and ZIP-based SOG files
src/loaders/Utils.js	Added SOG format detection for .sog file extensions
src/loaders/UncompressedSplatArray.js	Fixed spherical harmonics data placement in splat components
src/loaders/SceneFormat.js	Added SOG format enum value
src/index.js	Exported SogLoader for public API
src/Viewer.js	Integrated SOG loading support into main viewer

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