refactor(scene): group modules into role-based subfolders

Move the 30 flat modules under src/scene/ into six folders by role:
convert (entity→geometry), text (fonts/shaping), model (render models),
pick (hit-test/selection/grips/xclip), view (camera/transform/render),
cache (block + property caches). pipeline/ is unchanged.

Full path migration — all `scene::X` references become
`scene::<group>::X`, no compatibility re-exports. render.rs items that
were `pub(super)` (parent was scene) become `pub(in crate::scene)` to
keep their original scene-wide visibility.

No behavior change; build and tests are green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/entities/ole2frame.rs

@@ -4,9 +4,9 @@ use glam::Vec3;
 use crate::command::EntityTransform;
 use crate::entities::common::{center_grip, edit_prop as edit, ro_prop as ro, square_grip};
 use crate::entities::traits::TruckConvertible;
-use crate::scene::acad_to_truck::{TruckEntity, TruckObject};
-use crate::scene::object::{GripApply, GripDef, PropSection};
-use crate::scene::wire_model::SnapHint;
+use crate::scene::convert::acad_to_truck::{TruckEntity, TruckObject};
+use crate::scene::model::object::{GripApply, GripDef, PropSection};
+use crate::scene::model::wire_model::SnapHint;
 
 fn to_truck(ole: &Ole2Frame) -> TruckEntity {
     let x0 = ole.upper_left_corner.x;
@@ -184,7 +184,7 @@ impl crate::entities::traits::FallbackTess for Ole2Frame {
     fn fallback_geometry(
         &self,
         world_offset: [f64; 3],
-    ) -> crate::scene::tess_util::FallbackGeometry {
+    ) -> crate::scene::convert::tess_util::FallbackGeometry {
         // OLE objects carry a bounding rectangle in model space.
         // Render a simple X-through-rectangle placeholder.
         let [ox, oy, oz] = world_offset;