feat(gl): OpenGL 4.1 and the ludic.render3d renderer

`Gl.*` binds the whole OpenGL 4.1 core API — every entry point of the
platform gl3.h with every GL_* constant, generated by `ludic-dev glgen`
with per-call ABI thunks. Windowed builds get an NSOpenGLContext on the
existing window at Retina resolution; headless builds render into an
offscreen CGL context, so a program that uses Gl.* renders and
screenshots identically under the test harness. It links gl.ll, the
thunks and OpenGL.framework only when used; every other build stays
byte-identical.

packages/ludic.render3d is a physically based renderer written on that
surface: HDRI image-based lighting, GPU-generated terrain with scanned
PBR materials, CDLOD, cascaded shadows, glTF with skinning, instanced
vegetation with impostors, procedural grass, water, SSAO, and an HDR
pipeline with bloom, auto-exposure and ACES.

It also carries this session's work on it: the terrain at half its cost
(10.3 -> 5.4 ms of frame), the streaming hitch that got worse the longer
you played, a resize that emptied the world, and the packaging that lets
a game use the renderer from its own repository — `ludic assets`, the
material manifest shipping with the package, and shader lookup falling
back to the install root. See changes/ for each, with its numbers.

The camping game that drove all of it has moved out to its own
repository, Maroon Lake; examples/rendering/smooth.ludic stays as the
renderer's example here.

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

packages/ludic.render3d/shaders/water.vert

@@ -0,0 +1,12 @@
+layout(location = 0) in vec2 a_xz;
+uniform mat4 u_view;
+uniform mat4 u_proj;
+uniform float u_level;
+uniform vec2 u_center;
+uniform vec2 u_extent;
+out vec3 v_wpos;
+void main() {
+  vec3 p = vec3(u_center.x + a_xz.x * 2.0 * u_extent.x, u_level, u_center.y + a_xz.y * 2.0 * u_extent.y);   // the grid spans ±0.5
+  v_wpos = p;
+  gl_Position = u_proj * u_view * vec4(p, 1.0);
+}