feat(render3d): every shader variant as Vulkan SPIR-V, built ahead of time

Vulkan cannot compile GLSL when the game starts, so the programs render3d builds are listed
(shaders/variants.list, 45 of them, collected with R3D_PROGRAMS_LOG across the self-tests, the
screens, the viewpoints and the debug switches) and `ludic-dev shaders` compiles each into
shaders/spv/<id>.vert.spv and .frag.spv with a manifest of what the backend needs: each
stage's uniform block and member offsets, the samplers' bindings, the vertex inputs.

The GLSL is the renderer's own, assembled as programs.ludic assembles it, through glslang's
relaxed Vulkan mode, so gpu_uniform / u_* can write the same uniforms into a block on Vulkan.
Bindings are assigned by the tool (glslang's own numbering put several samplers of one stage
on binding 0): the vertex block is 0, the fragment block 1, samplers from 2 in name order,
shared across both stages. Every stage passes spirv-val; `ludic-dev test` rebuilds and compares
wherever the Vulkan SDK is installed.

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

packages/ludic.render3d/overlay.ludic

@@ -52,6 +52,7 @@ var ov_clip_w: int = 0
 var ov_clip_h: int = 0
 
 function overlay_init(font_dir: string) -> bool {
+  r3d_program_log("overlay.vert", "overlay.frag", "")
   ov_prog = gl_program("#version 410 core\n" + r3d_shader_file("overlay.vert"), "#version 410 core\n" + r3d_shader_file("overlay.frag"))
   if ov_prog == 0 { print("overlay: program failed");  return false }
   ov_vao = gl_vao()