feat(render3d): gpu.ludic - the seam for a second graphics API, and what the GPU can do

Render state (depth, blending, culling, colour writes, alpha-to-coverage, depth bias,
scissor) and uniforms go through gpu_* / u_* and nowhere else; OpenGL state is cached and
only changes reach the driver. Frames are bit-identical to before at the fixed viewpoints.
R3D_GFX=gl|vk or gpu_request chooses a backend, falling back to OpenGL with a reason.

gpu_caps_probe() asks Vulkan, on Windows, for the 1.3 floor, ray tracing, mesh shaders, the
NVIDIA RTX generation, Reflex and HDR colour spaces, for a game's settings to grey out what
a machine cannot use; R3D_CAPS pretends to be a given card for tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ludic.render3d/r3d.ludic

@@ -3,6 +3,7 @@
 # Import this one file; the game supplies scene_draw() / scene_draw_casters().
 # ============================================================================
 import "fmath.ludic"
+import "gpu.ludic"
 import "prof.ludic"
 import "programs.ludic"
 import "texture.ludic"