refactor: rename mislabeled scene files to match contents

Two names collided with the pick subsystem and misdescribed their files:

- scene/hittest.rs -> scene/camera_ops.rs. Its contents are camera/view
  operations (zoom, fit-all, named-view restore, camera<->document sync,
  per-tile grid/snap), not hit-testing — the real screen-space hit-test
  lives in scene/pick/hit_test.rs.
- scene/pick/selection.rs -> scene/pick/selection_state.rs. It holds only
  the SelectionState struct; the name clashed with scene/selection.rs
  (the Scene selection operations).

Callers are unaffected (the crate::scene::SelectionState re-export path is
unchanged). No behavior change.

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

src/scene/camera_ops.rs

@@ -1,4 +1,6 @@
-// Auto-split from scene/mod.rs. Pure text-move; behaviour unchanged.
+// Camera / view operations on `Scene`: zoom, fit-all, named-view restore,
+// camera<->document sync, and per-tile grid/snap. (The actual screen-space
+// hit-testing lives in `scene::pick::hit_test`.)
 use super::*;
 
 impl Scene {

src/scene/mod.rs

@@ -17,7 +17,7 @@ pub mod view;
 // blocks and/or free functions). Pure text-move from the original mod.rs.
 mod entity;
 mod group_layer;
-mod hittest;
+mod camera_ops;
 mod layout;
 mod modify;
 mod mspace;
@@ -53,7 +53,7 @@ pub use pipeline::viewcube::{
     hit_test, hit_test_cardinal, hover_id, CubeRegion, NudgeDir, VIEWCUBE_DRAW_PX, VIEWCUBE_PAD,
     VIEWCUBE_PX, VIEWCUBE_REGION_PX,
 };
-pub use pick::selection::SelectionState;
+pub use pick::selection_state::SelectionState;
 pub use model::wire_model::WireModel;
 
 use crate::command::EntityTransform;

src/scene/pick/mod.rs

@@ -1,5 +1,5 @@
 pub mod hit_test;
-pub mod selection;
+pub mod selection_state;
 pub mod grip;
 pub mod quadtree;
 pub mod xclip;