chore(task): archive 08-17-native-road-center-lines

.trellis/tasks/archive/2026-08/08-17-native-road-center-lines/implement.md

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+# Implementation Plan
+
+1. Add centre-dash constants and a pure native compiler routine based on the
+   shared bidirectional segment model and junction-trimmed centreline.
+2. Filter invalid, one-way, service, and control-marking-conflicting dashes;
+   record actionable diagnostics for invalid geometry only.
+3. Write `center_lines.geojson`, compilation/comparison counts, native build
+   records, required-layer checks, and Blender material adapter mapping.
+4. Add Workbench API state, Chinese toggle, summary count, rendering, and
+   source evidence for a selected centre dash.
+5. Add focused native and Workbench tests for generation, skips, control
+   avoidance, provenance, and file/API contracts.
+6. Run native/unit/workbench/build-stage tests, compile/check Nantaizi, then
+   validate `blender,cesium,preview --road-provider native` without `package`.
+
+## Rollback
+
+Choose `--road-provider osm2streets`; no legacy layer or published package is
+modified.