Add configurable MSAA anti-aliasing, update auth screen and terrain shader

- MSAA: conditional 2-att (off) vs 3-att (on) render pass with auto-resolve
- MSAA: multisampled color+depth images, query max supported sample count
- MSAA: .setMultisample() on all 25+ main-pass pipelines across 17 renderers
- MSAA: recreatePipelines() on every sub-renderer for runtime MSAA changes
- MSAA: Renderer::setMsaaSamples() orchestrates swapchain+pipeline+ImGui rebuild
- MSAA: Anti-Aliasing combo (Off/2x/4x/8x) in Video settings, persisted
- Update auth screen assets and terrain fragment shader

include/rendering/vk_context.hpp

@@ -71,6 +71,11 @@ public:
 
     bool isSwapchainDirty() const { return swapchainDirty; }
 
+    // MSAA
+    VkSampleCountFlagBits getMsaaSamples() const { return msaaSamples_; }
+    void setMsaaSamples(VkSampleCountFlagBits samples);
+    VkSampleCountFlagBits getMaxUsableSampleCount() const;
+
 private:
     bool createInstance(SDL_Window* window);
     bool createSurface(SDL_Window* window);
@@ -126,6 +131,15 @@ private:
     bool createDepthBuffer();
     void destroyDepthBuffer();
 
+    // MSAA resources
+    VkSampleCountFlagBits msaaSamples_ = VK_SAMPLE_COUNT_1_BIT;
+    VkImage msaaColorImage_ = VK_NULL_HANDLE;
+    VkImageView msaaColorView_ = VK_NULL_HANDLE;
+    VmaAllocation msaaColorAllocation_ = VK_NULL_HANDLE;
+
+    bool createMsaaColorImage();
+    void destroyMsaaColorImage();
+
     // ImGui resources
     VkRenderPass imguiRenderPass = VK_NULL_HANDLE;
     VkDescriptorPool imguiDescriptorPool = VK_NULL_HANDLE;