Refine sun rendering: remove white washout, add subtle atmospheric turbulence

- render sun with alpha blend while keeping moon additive glow
- add dedicated always-running sun haze timer (decoupled from moon phase cycling)
- constrain sun sprite with radial alpha mask and low-alpha discard to remove square artifact
- tune sun tint warmer without over-yellowing
- replace noisy/pulsing haze with slower flow-warp turbulence and lower amplitude

include/rendering/celestial.hpp

@@ -129,6 +129,7 @@ private:
     float blueChildPhase_ = 0.25f;  // 0.0-1.0 (0=new, 0.5=full) - secondary moon
     bool moonPhaseCycling = true;
     float moonPhaseTimer = 0.0f;  // Fallback for deltaTime mode (development)
+    float sunHazeTimer_ = 0.0f;   // Always-running timer for sun haze animation
     bool dualMoonMode_ = true;  // Default: render both moons (Azeroth-specific)
 
     // WoW lunar cycle constants (in game days)