fix(examples): use bundled Scenegraph flight snapshot

[ibgreen-openai]

Goal

Make the Scenegraph website example load reliably even when the OpenSky browser API is unavailable.

Changes

• Start from the bundled all.json flight snapshot so the example renders immediately.
• Try the live OpenSky endpoint once, then keep the bundled snapshot if the request is blocked by CORS or otherwise fails.
• Normalize data without mutating the imported snapshot.
• Remove the interval/update loop that could create repeated fetch failures.
• Rename the demo from “Realtime Flight Tracker” to “Flight Tracker” and document the fallback behavior.

This PR intentionally contains only example/data-source behavior. The ScenegraphLayer WebGPU port is split into a separate stacked PR.

Validation

• yarn lint (passes with existing repository warnings only)
• yarn test-website

[coveralls]

Coverage is 83.355% — codex/scenegraph-example-local-data into master. No base build found for master.