Migrates the toad example from SDL’s 2D Renderer API to SDL_GPU, keeping the same Character_Data / Sprite engine API and baked asset pipeline.
- Replaces CreateWindowAndRenderer / RenderTexture with GPU device + swapchain framing (begin_frame / end_frame)
- Adds sprite vertex/fragment GLSL shaders and compiled SPIR-V (shaders/sprite.*.glsl / .spv)
- Uploads atlas PNGs as GPUTexture via transfer buffer + copy pass (with fence sync)
- Draws sprites as UV quads (DrawGPUPrimitives) using atlas frame rects from char.json