Merge PR #300: tessellate hatch fills so navigation no longer flickers (#258)

External contribution by sLuCHa. Triangulates each hatch boundary once
(lyon even-odd, cached with the batch build) and rasterizes the triangles
instead of the per-fragment point-in-polygon test, removing the screen-fill
overdraw + boundary raycast that forced the flicker-causing interaction LOD
(now default off behind OCS_HATCH_LOD). Precision preserved (triangles in the
same world_origin-relative frame + RTE path); untessellatable boundaries fall
back to the old AABB-quad + in_polygon path (poly_test=1).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/view/render.rs

@@ -1131,7 +1131,7 @@ impl Scene {
             // actively moving; the scene-render cache holds the full-quality
             // (hatched) frame once it settles. Only applied to the on-screen
             // Model / paper content — the paper *sheet* keeps its fills.
-            skip_hatch: !inst.paper_sheet && self.navigating_lod(),
+            skip_hatch: self.hatch_lod_enabled() && !inst.paper_sheet && self.navigating_lod(),
             geometry_epoch: self.geometry_epoch,
             camera_generation: self.camera_generation,
             wire_content_id,