examples: apply real texture assets to multi-mesh examples

- meshes/cube: procedural checkerboard -> uv_texture.jpg (8x8 UV grid)
- meshes/pbr: floor -> ground.jpeg, bump cube -> cave.jpg + caveNormal.jpg
  (normal map pre-encoded via sRGB OETF to cancel the GPU sRGB decode)
- lights/shadow: ground -> ground.jpeg, cube -> uv_texture.jpg
- effects/demo: ground -> ground.jpeg, cube -> uv_texture.jpg
- effects/fog: ground -> ground.jpeg (tiled 80x80), cubes -> stonewall.jpg
- effects/dof: ground -> ground.jpeg, cubes -> uv_texture.jpg
- cameras/culling: shared cube mesh -> uv_texture.jpg
- add lib/examples/assets/textures/ (19 assets, 6.5 MB)
- document assets + usage in examples READMEs, docs/user/examples.md,
  docs/user/meshes/materials.md (CARGO_MANIFEST_DIR pattern, sRGB caveat)

lib/examples/effects/dof.rs

@@ -35,9 +35,13 @@ use wsg_lib::app::AppBuilder;
 use wsg_lib::camera::CameraController;
 use wsg_lib::core::{DoFConfig, ToneMapper, Transform};
 use wsg_lib::mesh::{cube, icosphere, plane};
+use wsg_lib::resources::Texture;
 use wsg_lib::AppHandler;
 use wsg_lib::utils::WsgError;
 
+/// Texture asset directory, resolved against the crate root so the example works from any CWD.
+const TEXTURES: &str = concat!(env!("CARGO_MANIFEST_DIR"), "/examples/assets/textures");
+
 struct DoFDemo {
     camera: CameraController,
 }
@@ -48,9 +52,33 @@ impl AppHandler for DoFDemo {
             .register_shader("standard", wsg_lib::utils::STANDARD_SHADER_PATH)
             .unwrap();
 
+        // Textured ground + cubes: bokeh blur reads much better on textured surfaces.
+        // ground.jpeg tiles across the 80×80 floor (Repeat sampler); uv_texture.jpg on the cubes.
+        let (device, queue) = {
+            let ctx = app.context();
+            (ctx.device.clone(), ctx.queue.clone())
+        };
+        let ground_tex =
+            Texture::from_file(&device, &queue, "ground", &format!("{TEXTURES}/ground.jpeg")).unwrap();
+        app.scene.add_texture("ground_texture", ground_tex).unwrap();
+        app.scene
+            .add_material_texture("ground_mat", "standard", "ground_texture")
+            .unwrap();
+        let uv_tex = Texture::from_file(
+            &device,
+            &queue,
+            "uv_atlas",
+            &format!("{TEXTURES}/uv_texture.jpg"),
+        )
+        .unwrap();
+        app.scene.add_texture("uv_texture", uv_tex).unwrap();
+        app.scene
+            .add_material_texture("cube_mat", "standard", "uv_texture")
+            .unwrap();
+
         // Ground plane.
         app.scene
-            .create_mesh("ground_mesh", plane(80.0, 80.0, 1, 1), None)
+            .create_mesh("ground_mesh", plane(80.0, 80.0, 1, 1), Some("ground_mat"))
             .unwrap();
         app.scene
             .add_entity_with_transform(
@@ -62,7 +90,7 @@ impl AppHandler for DoFDemo {
 
         // Row of cubes receding along -Z (distance ≈ 2 to 25 from camera at dist=8).
         app.scene
-            .create_mesh("cube_mesh", cube(1.0), None)
+            .create_mesh("cube_mesh", cube(1.0), Some("cube_mat"))
             .unwrap();
 
         for i in 0..20 {