feat(dome): Adding Skydome as option for skybox

[marcteys]

I think it's quite useful to allow user to load skydome. It is particularly relevant when loading cleaned-up grounded objects ( example a building without it's context).

Summary

Unifies skybox/skydome configuration under background.skybox, adds dome projection support, and refreshes the example with v2 settings and a default orbit anim track.

Changes

• Replaced skydomeUrl with a single background.skybox object (url, projection, scale, center) in the v2 schema.
• Added skyprojection query param and kept skydome as a backwards‑compatible alias.
• Implemented dome rendering via a DomeGeometry mesh (background‑only) and expanded camera far clip when a dome is present.
• Made the dome world‑aligned (uses the configured center, no camera‑follow).
• Updated example/settings.json to v2 and included a looping orbit anim track for a better out‑of‑box demo.

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You can test this PR with the example here: https://github.com/preserve-archi/supersplat-viewer-skyDomeExample