Add a CI-safe data-validation test for the issue #1052 vendor-shop
regions. Parses Distribution/Data/regions.json (copied beside the test
assembly) without client map files and asserts known vendor coordinates
resolve to a shop-specific region nested under the town, that shop
regions are structurally valid (non-empty area, resolvable parent,
unique names per map), and that they do not overlap other regions.
Refs #1052
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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