feat: add native road marking semantics

.trellis/tasks/08-17-native-road-marking-semantics/implement.md

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+# Implementation
+
+1. Extend override validation and native marking generation for explicit
+   double-yellow centre lines and per-side edge-line styles.
+2. Extend the Chinese Workbench selection/form flow without adding another
+   editor or output format.
+3. Add compiler and Workbench regression coverage for valid and invalid
+   payloads, generated geometry, and layer adapter completeness.
+4. Compile/check Nantaizi, run native/Workbench/build-stage/Blender tests,
+   then run the native Blender/Cesium/preview chain.