Merge per-chunk water surfaces, restore incremental tile finalization, and pin main thread CPU affinity

Water deduplication: merge per-chunk water surfaces into per-tile surfaces
to reduce Vulkan descriptor set usage from ~8900 to ~100-200. Uses hybrid
approach — groups with ≤4 chunks stay per-chunk (preserving shore detail),
larger groups merge into 128×128 tile-wide surfaces.

Re-add incremental tile finalization state machine (reverted in 9b90ab0)
to spread GPU uploads across frames and prevent city stuttering.

Pin main thread to CPU core 0 and exclude worker threads from core 0
to reduce scheduling jitter on the render/game loop.

include/rendering/water_renderer.hpp

@@ -160,7 +160,7 @@ private:
     VkDescriptorSetLayout sceneSetLayout = VK_NULL_HANDLE;
     VkDescriptorPool sceneDescPool = VK_NULL_HANDLE;
     VkDescriptorSet sceneSet = VK_NULL_HANDLE;
-    static constexpr uint32_t MAX_WATER_SETS = 2048;
+    static constexpr uint32_t MAX_WATER_SETS = 16384;
 
     VkSampler sceneColorSampler = VK_NULL_HANDLE;
     VkSampler sceneDepthSampler = VK_NULL_HANDLE;