Add RegionSpawner.Json.cs with a `region` shadow property (serializes
SpawnRegion.Name) and OnAfterJsonDeserialize override that resolves the
region by name using _jsonMap from BaseSpawner. Mark RegionSpawner with
[JsonDiscoverableType] and [JsonConstructor] on its parameterless ctor
so SpawnerJsonSerializer discovers it for STJ polymorphism.
Add RegionSpawnerRoundTripTests: create+register a test BaseRegion on
Felucca (game regions are not loaded in the test environment), serialize
a RegionSpawner, assert $type and region name in JSON, deserialize, and
assert SpawnRegion.Name round-trips correctly. RED → GREEN confirmed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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