Add shader-driven tree beautification: wind sway, SSS, color variation, AO

- Vertex wind animation: 3-layer displacement (trunk/branch/leaf) with
  quadratic height scaling so bases stay grounded
- Shadow pass: matching vertex displacement split into foliage/non-foliage
  passes, removed UV-wiggle approach
- Leaf subsurface scattering: warm backlit glow when looking toward sun
- Per-instance color variation: hue/brightness from position hash via flat
  varying to avoid interpolation flicker
- Canopy ambient occlusion: height-based darkening of tree interiors
- Detail normal perturbation: UV-only procedural normals to break flat cards
- Bayer 4x4 ordered dither replacing sin-hash noise for alpha edges
- Foliage skips shadow map sampling and specular to prevent flicker from
  swaying geometry sampling unstable shadow/highlight values

include/rendering/m2_renderer.hpp

@@ -251,7 +251,7 @@ public:
     /**
      * Render depth-only pass for shadow casting
      */
-    void renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSpaceMatrix);
+    void renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSpaceMatrix, float globalTime = 0.0f);
 
     /**
      * Render M2 particle emitters (point sprites)