refactor: finish OST f64 integration; drop vestigial _f64 suffixes

- Object-snap-tracking points now project through the relative-to-eye path
  (view_proj_rte + eye) instead of the full view-projection, so they stay
  precise at UTM-scale coordinates — the last consumer of the legacy full
  view_proj outside the CPU frustum-cull / scissor path.
- Rename Camera::project_f64 → project and unproject_on_plane_f64 →
  unproject_on_plane: the f32 twins are gone, so the disambiguating suffix
  is vestigial. eye_f64 keeps its name — the f32 eye() still builds the
  view matrices.
- Remove stale #[allow(dead_code)] from eye_f64 / project / unproject_on_plane
  (all live now).

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

src/scene/pick/grip.rs

@@ -43,7 +43,7 @@ pub fn grips_to_screen(
             // Project from the f64 grip position via the relative-to-eye path so
             // the grip stays glued to the wire at UTM-scale coordinates (an
             // `as_vec3` cast first would quantize it ~0.5 m off at high zoom).
-            let screen = match camera.project_f64(g.world, bounds) {
+            let screen = match camera.project(g.world, bounds) {
                 Some(p) => Point::new(bounds.x + p.x, bounds.y + p.y),
                 None => Point::new(f32::NAN, f32::NAN),
             };
@@ -115,7 +115,7 @@ pub fn find_hit_grip(
     let mut best: Option<(usize, bool, DVec3)> = None;
 
     for g in grips {
-        let Some(screen) = camera.project_f64(g.world, bounds) else {
+        let Some(screen) = camera.project(g.world, bounds) else {
             continue;
         };
         let screen = Point::new(screen.x, screen.y);
@@ -131,7 +131,7 @@ pub fn find_hit_grip(
 }
 
 /// Project an f64 world point with an explicit relative-to-eye `(view_rot,
-/// eye)` pair — the camera-less form of `Camera::project_f64`. Used by the
+/// eye)` pair — the camera-less form of `Camera::project`. Used by the
 /// in-viewport editing path, which supplies a *composed* model→screen view
 /// (see `Scene::composed_viewport_view`) instead of a real camera.
 fn project_rte(world: DVec3, view_rot: Mat4, eye: DVec3, bounds: Rectangle) -> Option<Vec2> {