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/shaders/face3d.wgsl

@@ -6,7 +6,6 @@
 
 struct Uniforms {
     view_proj:           mat4x4<f32>,
-    camera_pos:          vec4<f32>,
     viewport_size:       vec2<f32>,
     world_per_pixel:     f32,
     lwdisplay_enable:    f32,

src/shaders/hatch.wgsl

@@ -14,7 +14,6 @@
 
 struct Uniforms {
     view_proj:           mat4x4<f32>,
-    camera_pos:          vec4<f32>,
     viewport_size:       vec2<f32>,
     world_per_pixel:     f32,
     lwdisplay_enable:    f32,

src/shaders/hatch_batched.wgsl

@@ -19,7 +19,6 @@
 
 struct Uniforms {
     view_proj:           mat4x4<f32>,
-    camera_pos:          vec4<f32>,
     viewport_size:       vec2<f32>,
     world_per_pixel:     f32,
     lwdisplay_enable:    f32,

src/shaders/image.wgsl

@@ -5,7 +5,6 @@
 // Must match the shared `Uniforms` struct (scene::pipeline::uniforms, 112 B).
 struct Uniforms {
     view_proj:          mat4x4<f32>,
-    camera_pos:         vec4<f32>,
     viewport_size:      vec2<f32>,
     world_per_pixel:    f32,
     lwdisplay_enable:   f32,

src/shaders/mesh.wgsl

@@ -11,7 +11,6 @@
 
 struct Uniforms {
     view_proj:           mat4x4<f32>,
-    camera_pos:          vec4<f32>,
     viewport_size:       vec2<f32>,
     world_per_pixel:     f32,
     lwdisplay_enable:    f32,

src/shaders/wire.wgsl

@@ -15,7 +15,6 @@
 
 struct Uniforms {
     view_proj:        mat4x4<f32>,
-    camera_pos:       vec4<f32>,
     viewport_size:    vec2<f32>,
     world_per_pixel:  f32,
     // LWDISPLAY toggle: 0.0 = force 1 px (half_width 0.5), 1.0 = use the