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/scene/pipeline/face3d_gpu.rs

@@ -18,7 +18,7 @@
 // render pass send the 3D side through a depth-only pipeline for
 // HiddenLine while keeping the 2D side fully visible.
 
-use crate::scene::wire_model::WireModel;
+use crate::scene::model::wire_model::WireModel;
 use iced::wgpu;
 use iced::wgpu::util::DeviceExt;
 

src/scene/pipeline/hatch_batched_gpu.rs

@@ -35,7 +35,7 @@
 // InstanceBuffer + Boundary + Family + Dash. Both stages share group
 // 1 with `read_only` access.
 
-use crate::scene::hatch_model::{HatchModel, HatchPattern, PatFamily};
+use crate::scene::model::hatch_model::{HatchModel, HatchPattern, PatFamily};
 use iced::wgpu;
 use iced::wgpu::util::DeviceExt;
 

src/scene/pipeline/hatch_gpu.rs

@@ -5,7 +5,7 @@
 //   binding 1 — BoundaryData      (16384 bytes) boundary polygon vertices
 //   binding 2 — FamilyBatchData   (1296 bytes)  up to 16 line families + 128 dash values
 
-use crate::scene::hatch_model::{HatchModel, HatchPattern, PatFamily, MAX_HATCH_BOUNDARY_VERTS};
+use crate::scene::model::hatch_model::{HatchModel, HatchPattern, PatFamily, MAX_HATCH_BOUNDARY_VERTS};
 use iced::wgpu;
 use iced::wgpu::util::DeviceExt;
 

src/scene/pipeline/image_gpu.rs

@@ -5,7 +5,7 @@
 //   binding 1 — sampler           (bilinear filtering)
 //   binding 2 — ImageParams       (opacity uniform, 16 bytes)
 
-use crate::scene::image_model::ImageModel;
+use crate::scene::model::image_model::ImageModel;
 use iced::wgpu;
 use iced::wgpu::util::DeviceExt;
 

src/scene/pipeline/mesh_gpu.rs

@@ -7,7 +7,7 @@
 //                                ------
 //                                 40 B / vertex
 
-use crate::scene::mesh_model::{MeshLodSet, MeshModel};
+use crate::scene::model::mesh_model::{MeshLodSet, MeshModel};
 use iced::wgpu;
 use iced::wgpu::util::DeviceExt;
 

src/scene/pipeline/mod.rs

@@ -19,10 +19,10 @@ pub use uniforms::Uniforms;
 pub use viewcube::ViewCubePipeline;
 pub use wire_gpu::WireGpu;
 
-use crate::scene::hatch_model::HatchModel;
-use crate::scene::image_model::ImageModel;
-use crate::scene::mesh_model::MeshLodSet;
-use crate::scene::wire_model::WireModel;
+use crate::scene::model::hatch_model::HatchModel;
+use crate::scene::model::image_model::ImageModel;
+use crate::scene::model::mesh_model::MeshLodSet;
+use crate::scene::model::wire_model::WireModel;
 
 /// MSAA sample count for the main drawing pipelines.
 const MSAA_SAMPLES: u32 = 4;

src/scene/pipeline/uniforms.rs

@@ -1,4 +1,4 @@
-use crate::scene::camera::Camera;
+use crate::scene::view::camera::Camera;
 use iced::Rectangle;
 
 #[derive(Copy, Clone, Debug, bytemuck::Pod, bytemuck::Zeroable)]

src/scene/pipeline/wire_gpu.rs

@@ -22,7 +22,7 @@
 //                                          ------
 //                                           76 B / instance
 
-use crate::scene::wire_model::WireModel;
+use crate::scene::model::wire_model::WireModel;
 use iced::wgpu;
 use rayon::prelude::*;