refactor(render): drop dead camera_pos from the shared uniform

No GPU pipeline reads camera_pos any more — lighting and all transforms
moved to the relative-to-eye path (view_rot + eye_high/eye_low). Remove
the field from the shared Uniforms and every shader struct, plus the now
unused Camera::position_vec4. view_proj stays: the CPU frustum-cull /
scissor / LOD passes still project offset-relative AABBs with it (it is
no longer part of any GPU draw).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/scene/view/camera.rs

@@ -228,9 +228,6 @@ impl Camera {
         }
     }
 
-    pub fn position_vec4(&self) -> glam::Vec4 {
-        glam::Vec4::from((self.eye(), 0.0))
-    }
 
     // ── ViewCube rotation matrix ───────────────────────────────────────────