feat: add NASA GIBS surface temperature layer with year playback

[Udaydsmls]

Surface Temperature layer (NASA GIBS)

Adds a keyless Surface Temperature layer under Weather. It plays back MODIS Terra monthly land-surface-temperature means one year at a time.

• Playback: the months crossfade smoothly, and the overlay's opacity stays steady during each blend.
• On-map panel: shows the current month, play/pause, NASA's colour scale, a year scale (2000 to now) and a month scale. Clicking a year loads it without blanking the globe; clicking a month glides to it.
• Click-to-read: reads the published tile pixel against NASA's colour map, so the value is the product's own reading, not an estimate. The reading stays pinned and updates each month.
• Gaps are stated: unpublished months are skipped, and cloud or water reports no value.

Notes

• Share-link token 0, from npm run layer-token:next. Re-run it if another new layer merges first.
• The token ledger tests now read free digits from the ledger instead of assuming 0/3 are free, so any PR that adds a layer no longer breaks them.
• The readout card uses the world-overlay host, not a Cesium label.

Testing

npm test, npm run format:check, npm run check:boundaries and npm run layer-token:check -- --base-ref origin/main all pass.

[Udaydsmls]

@bilawalsidhu and @samehkhamis let me know your thoughts on this feature.

[kvnloo]

The click-to-read path has one measurement-vs-rendering distinction I would fix.

sampler.js reports:

resolutionM: metresPerPixel(latitude, GIBS_MAX_LEVEL)

and the card renders that as e.g. ~2.4 km pixel.

That is the GIBS Web Mercator tile pixel size, not the native resolution of the MODIS monthly LST product. NASA describes MOD11C3 as a 0.05° Climate Modeling Grid, about 5.6 km at the equator:
https://data.nasa.gov/dataset/modis-terra-land-surface-temperature-emissivity-monthly-l3-global-0-05deg-cmg-v061-8e12e

GIBS can resample that product into a finer display tile grid; a finer PNG pixel does not create a finer temperature measurement.

I would either:

• report the native product resolution (~0.05° / ~5.6 km nominal) in the readout; or
• label the current number explicitly as rendered tile pixel, separate from source measurement resolution.

Related small doc nit: dataCredits.js currently calls this an "8-day composite", while this layer is using the monthly daytime product.