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).
