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/mount_dust.hpp

@@ -18,6 +18,7 @@ public:
 
     bool initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout);
     void shutdown();
+    void recreatePipelines();
 
     // Spawn dust particles at mount feet when moving on ground
     void spawnDust(const glm::vec3& position, const glm::vec3& velocity, bool isMoving);