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/m2_renderer.hpp

@@ -281,6 +281,8 @@ public:
     double getQueryTimeMs() const { return queryTimeMs; }
     uint32_t getQueryCallCount() const { return queryCallCount; }
 
+    void recreatePipelines();
+
     // Stats
     bool isInitialized() const { return initialized_; }
     uint32_t getModelCount() const { return static_cast<uint32_t>(models.size()); }