feat: Add legacy shaders, model I/O, and project panel functionality

- Introduced `legacy-shaders.js` containing vertex and fragment shaders for rendering.
- Implemented `model-io.js` for parsing and encoding GLB files, ensuring compatibility with glTF 2.0.
- Created `project-panel.js` to manage project resources and survey overlays, enhancing user interaction.
- Added `solar.js` for calculating solar positions based on UTC time, latitude, and longitude.
- Developed `three-renderer.js` as a standard backend for Three.js, managing scene rendering and material synchronization.
- Included a new GLB model `dum.glb` for testing and demonstration purposes.
- Established `data_checks.mjs` for validating model data and ensuring integrity of assets.
- Created `prepare_export.py` to facilitate Blender GLB exports, maintaining material and node references.
- Added `vendor_three.py` to download and configure a local version of Three.js for the project.

locenice2/THIRD_PARTY.txt

@@ -0,0 +1,8 @@
+Three.js r180 / 0.180.0 is loaded from jsDelivr by default. It is not bundled here.
+Source: https://github.com/mrdoob/three.js/tree/r180
+License: MIT, Copyright (c) 2010-2025 three.js authors.
+The optional vendor downloader fetches and preserves the upstream LICENSE.
+
+User supplied model, drawings, catalogue samples and reference photographs:
+provided for this project. No third-party asset ownership is claimed.
+Do not treat these files as a separately licensed general-purpose asset library.