Enhanced sky atmosphere with DBC-driven colors, sun lighting, and zone weather

- Skybox now uses DBC sky colors (skyTop/skyMiddle/skyBand1/skyBand2) instead
  of hardcoded C++ color curves, with 3-band gradient and Rayleigh/Mie scattering
- Clouds receive sun direction for lit edges, self-shadowing, and silver lining
- Fixed sun quad box artifact with proper edge fade in celestial shader
- Lens flare attenuated by fog, cloud density, and weather intensity
- Replaced garish green/purple lens flare ghosts with warm natural palette
- Added zone-based weather system for single-player mode with per-zone rain/snow
  configuration, probability-based activation, and smooth intensity transitions
- Server SMSG_WEATHER remains authoritative when connected to a server

include/rendering/lens_flare.hpp

@@ -47,8 +47,13 @@ public:
      * @param camera The camera to render from
      * @param sunPosition World-space sun position
      * @param timeOfDay Current time (0-24 hours)
+     * @param fogDensity Fog density 0-1 (attenuates flare)
+     * @param cloudDensity Cloud density 0-1 (attenuates flare)
+     * @param weatherIntensity Weather intensity 0-1 (rain/snow attenuates flare)
      */
-    void render(VkCommandBuffer cmd, const Camera& camera, const glm::vec3& sunPosition, float timeOfDay);
+    void render(VkCommandBuffer cmd, const Camera& camera, const glm::vec3& sunPosition,
+                float timeOfDay, float fogDensity = 0.0f, float cloudDensity = 0.0f,
+                float weatherIntensity = 0.0f);
 
     /**
      * @brief Enable or disable lens flare rendering