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/ui/auth_screen.hpp

@@ -1,11 +1,13 @@
 #pragma once
 
 #include "auth/auth_handler.hpp"
-#include "rendering/video_player.hpp"
+#include <vulkan/vulkan.h>
 #include <string>
 #include <vector>
 #include <functional>
 
+namespace wowee { namespace rendering { class VkContext; } }
+
 namespace wowee { namespace ui {
 
 /**
@@ -103,9 +105,18 @@ private:
     void upsertCurrentServerProfile(bool includePasswordHash);
     std::string currentExpansionId() const;
 
-    // Background video
-    bool videoInitAttempted = false;
-    rendering::VideoPlayer backgroundVideo;
+    // Background image (Vulkan)
+    bool bgInitAttempted = false;
+    bool loadBackgroundImage();
+    void destroyBackgroundImage();
+    rendering::VkContext* bgVkCtx = nullptr;
+    VkImage bgImage = VK_NULL_HANDLE;
+    VkDeviceMemory bgMemory = VK_NULL_HANDLE;
+    VkImageView bgImageView = VK_NULL_HANDLE;
+    VkSampler bgSampler = VK_NULL_HANDLE;
+    VkDescriptorSet bgDescriptorSet = VK_NULL_HANDLE;
+    int bgWidth = 0;
+    int bgHeight = 0;
 
     bool musicInitAttempted = false;
     bool musicPlaying = false;

include/ui/game_screen.hpp

@@ -102,6 +102,7 @@ private:
     bool pendingAutoLoot = false;
     bool pendingUseOriginalSoundtrack = true;
     int pendingGroundClutterDensity = 100;
+    int pendingAntiAliasing = 0;  // 0=Off, 1=2x, 2=4x, 3=8x
 
     // UI element transparency (0.0 = fully transparent, 1.0 = fully opaque)
     float uiOpacity_ = 0.65f;
@@ -110,6 +111,7 @@ private:
     bool minimapNpcDots_ = false;
     bool minimapSettingsApplied_ = false;
     bool volumeSettingsApplied_ = false;  // True once saved volume settings applied to audio managers
+    bool msaaSettingsApplied_ = false;   // True once saved MSAA setting applied to renderer
 
     // Mute state: mute bypasses master volume without touching slider values
     bool soundMuted_ = false;