fix: return UINT32_MAX from findMemType on failure, add [[nodiscard]]

The findMemType/findMemoryType helper in auth_screen, loading_screen,
and vk_context returned 0 on failure — a valid memory type index.
Changed to return UINT32_MAX and log an error, so vkAllocateMemory
receives an invalid index and fails cleanly rather than silently
using the wrong memory type.

Add [[nodiscard]] to VkBuffer::uploadToGPU/createMapped and
VkContext::initialize/recreateSwapchain so callers that ignore
failure are flagged at compile time. Suppress with (void) cast at
3 call sites where failure is non-actionable (resize best-effort).

src/rendering/loading_screen.cpp

@@ -78,7 +78,8 @@ static uint32_t findMemoryType(VkPhysicalDevice physDevice, uint32_t typeFilter,
             return i;
         }
     }
-    return 0;
+    LOG_ERROR("LoadingScreen: no suitable memory type found");
+    return UINT32_MAX;
 }
 
 bool LoadingScreen::loadImage(const std::string& path) {
@@ -420,7 +421,7 @@ void LoadingScreen::render() {
             int w = 0, h = 0;
             SDL_GetWindowSize(sdlWindow, &w, &h);
             if (w > 0 && h > 0) {
-                vkCtx->recreateSwapchain(w, h);
+                (void)vkCtx->recreateSwapchain(w, h);
             }
         }