Add water refraction toggle with per-frame scene history

Fix VK_ERROR_DEVICE_LOST crash by allocating per-frame scene history
images (color + depth) instead of a single shared image that raced
between frames in flight. Water refraction can now be toggled via
Settings > Video > Water Refraction.

Without refraction: richer blue base colors, animated caustic shimmer,
and normal-based color shifts give the water visible life. With
refraction: clean screen-space refraction with Beer-Lambert absorption.
Disabling clears scene history to black for immediate fallback.

include/rendering/renderer.hpp

@@ -256,6 +256,9 @@ public:
     bool areShadowsEnabled() const { return shadowsEnabled; }
     void setMsaaSamples(VkSampleCountFlagBits samples);
 
+    void setWaterRefractionEnabled(bool enabled);
+    bool isWaterRefractionEnabled() const;
+
 private:
     void applyMsaaChange();
     VkSampleCountFlagBits pendingMsaaSamples_ = VK_SAMPLE_COUNT_1_BIT;