FarlandsTweaks Core 1.3 - Stellara biome compatibility

Adds one uniquely named Stellara skybox at
data/stellara/skyboxes/farlands_fallback.json and a client reload listener.

The fallback keeps the forest theme, time window and nine layers, but has no
explicit biome allowlist. It therefore matches every biome in dimensions
supported by Stellara. Its weight is 1, below every original nighttime theme,
so all specialized skyboxes win where their conditions match. Stellara's own
forest.json is untouched and resource-pack ordering cannot undo this fallback.

Client assets include copies of Stellara's ten original JSON definitions and
the fallback. This allows Stellara's parser to populate its client registry
even when connected to a remote server that does not install Stellara.
