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)

docs/user/examples.md

@@ -11,8 +11,8 @@ README (description + how to run): [`meshes/`](../../lib/examples/meshes/README.
 | Example | Folder | What it shows | How to run | Corresponding page |
 |---------|--------|---------------|------------|--------------------|
 | `simple` | meshes | A 2D quad with vertex colors, unlit mode (~30 lines) | `cargo run -p wsg-lib --example simple` | [Quickstart](quickstart.md), [Materials](meshes/materials.md) |
-| `cube` | meshes | A rotating cube: point + spot light, checkerboard texture, procedural normal map, orbit/zoom | `cargo run -p wsg-lib --example cube` | [Meshes](meshes/meshes.md), [Materials](meshes/materials.md), [Lights](lights/lights.md) |
-| `pbr` | meshes | A procedural PBR material (metal/roughness) + a checker diffuse | `cargo run -p wsg-lib --example pbr` | [Materials](meshes/materials.md) |
+| `cube` | meshes | A rotating cube: point + spot light, `uv_texture.jpg` UV-atlas texture | `cargo run -p wsg-lib --example cube` | [Meshes](meshes/meshes.md), [Materials](meshes/materials.md), [Lights](lights/lights.md) |
+| `pbr` | meshes | PBR materials (metal/roughness) + real textures: `cave.jpg` albedo, `caveNormal.jpg` normal map, `ground.jpeg` floor | `cargo run -p wsg-lib --example pbr` | [Materials](meshes/materials.md) |
 | `import` | meshes | Wavefront **OBJ** import (CLI: file path as argument, procedural cube as fallback) | `cargo run -p wsg-lib --example import --features import-obj -- model.obj` | [Geometry sources](meshes/sources.md) |
 | `manual` | meshes | **Advanced**: the full manual workflow — buffers, pipelines, command encoding, no helpers | `cargo run -p wsg-lib --example manual` | [ARCHI_APP](../tech/ARCHI_APP.md), [FRAME_LOOP](../tech/FRAME_LOOP.md) |
 | `shadow` | lights | Shadow mapping: the classic pitfall — the packed-index shadow caster | `cargo run -p wsg-lib --example shadow` | [Shadows](lights/shadows.md) |
@@ -27,6 +27,13 @@ README (description + how to run): [`meshes/`](../../lib/examples/meshes/README.
 | `fog` | effects | Distance fog, 3 modes switchable at runtime (linear / exponential / exp²) | `cargo run -p wsg-lib --example fog` | [Fog](effects/fog.md) |
 | `dof` | effects | Depth of field: Gaussian blur scaled by defocus distance, cinematic bokeh; focus presets 1-4 + continuous zoom | `cargo run -p wsg-lib --example dof` | [DoF](effects/dof.md) |
 
+> **Texture assets**: the multi-mesh examples use real image files from
+> [`lib/examples/assets/textures/`](../../lib/examples/assets/textures/) (see the
+> [Texture assets](../../lib/examples/README.md#texture-assets) section there for the full
+> table): `uv_texture.jpg` (UV atlas visualization), `ground.jpeg` (tiled floor albedo),
+> `stonewall.jpg`, and the `cave.jpg` + `caveNormal.jpg` albedo/normal pair. Paths are
+> resolved against `CARGO_MANIFEST_DIR`, so the examples run from any working directory.
+
 ## The `manual` example: bypassing the helpers
 
 [`manual.rs`](../../lib/examples/meshes/manual.rs) renders a rotating cube with **no