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/sharpen.frag

@@ -0,0 +1,21 @@
+// luma unsharp mask + film grain, on the final LDR image
+in vec2 v_uv;
+out vec4 o_color;
+uniform sampler2D u_src;
+uniform vec2 u_texel;
+uniform float u_amount;
+uniform float u_grain;
+float hash(vec2 p) { return fract(sin(dot(p, vec2(12.9898, 78.233))) * 43758.5453); }
+float luma(vec3 c) { return dot(c, vec3(0.299, 0.587, 0.114)); }
+void main() {
+  vec3 c = texture(u_src, v_uv).rgb;
+  vec3 n = texture(u_src, v_uv + vec2(0, u_texel.y)).rgb, s = texture(u_src, v_uv - vec2(0, u_texel.y)).rgb;
+  vec3 e = texture(u_src, v_uv + vec2(u_texel.x, 0)).rgb, w = texture(u_src, v_uv - vec2(u_texel.x, 0)).rgb;
+  float lc = luma(c);
+  float lb = (luma(n) + luma(s) + luma(e) + luma(w) + lc * 4.0) / 8.0;
+  float d = clamp((lc - lb) * u_amount, -0.08, 0.08);
+  vec3 col = c * (1.0 + d / max(lc, 1e-3));
+  float g = (hash(v_uv * 1731.0 + fract(u_time)) - 0.5) * u_grain;
+  col += g * (0.6 + 0.4 * (1.0 - lc));
+  o_color = vec4(clamp(col, 0.0, 1.0), 1.0);
+}