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/tonemap.frag

@@ -0,0 +1,47 @@
+// exposure -> ACES -> vignette -> sRGB, with dithering
+in vec2 v_uv;
+out vec4 o_color;
+uniform sampler2D u_hdr;
+uniform sampler2D u_bloom;
+uniform sampler2D u_ao;
+uniform float u_ao_strength;
+uniform float u_gi_strength;
+uniform vec3 u_wb;                // white balance multiplier
+uniform vec3 u_lift;
+uniform vec3 u_gain;
+uniform float u_exposure;
+uniform sampler2D u_adapt;        // the GPU's adapted exposure (adapt.frag), 1x1
+uniform float u_auto;             // 1: use it, 0: u_exposure as set
+uniform float u_bloom_strength;
+uniform float u_vignette;
+uniform float u_saturation;
+uniform float u_contrast;
+vec3 aces(vec3 x) {
+  const float a = 2.51, b = 0.03, c = 2.43, d = 0.59, e = 0.14;
+  return clamp((x * (a * x + b)) / (x * (c * x + d) + e), 0.0, 1.0);
+}
+float hash(vec2 p) { return fract(sin(dot(p, vec2(12.9898, 78.233))) * 43758.5453); }
+void main() {
+  vec3 hdr = sane(texture(u_hdr, v_uv).rgb);
+  vec4 gi = texture(u_ao, v_uv);
+  hdr *= mix(1.0, gi.a, u_ao_strength);
+  // the indirect bounce arrives in the surface's own hue (no albedo buffer in a forward renderer)
+  float l = dot(hdr, vec3(0.2126, 0.7152, 0.0722));
+  hdr += gi.rgb * (hdr / max(l, 1e-3)) * u_gi_strength;
+  vec3 bloom = texture(u_bloom, v_uv).rgb;
+  float exposure = mix(u_exposure, texture(u_adapt, vec2(0.5)).r, u_auto);
+  vec3 c = (hdr + bloom * u_bloom_strength) * exposure * u_wb;
+  // filmic contrast around mid grey in log space
+  c = max(c, vec3(0.0));
+  c = pow(c / 0.18, vec3(u_contrast)) * 0.18;
+  c = aces(c);
+  // lift / gain grade in display space
+  c = c * u_gain + u_lift * (1.0 - c);
+  float lum = dot(c, vec3(0.2126, 0.7152, 0.0722));
+  c = mix(vec3(lum), c, u_saturation);
+  vec2 q = v_uv * 2.0 - 1.0;
+  c *= 1.0 - u_vignette * dot(q, q) * 0.5;
+  c = pow(c, vec3(1.0 / 2.2));
+  c += (hash(gl_FragCoord.xy) - 0.5) / 255.0;
+  o_color = vec4(c, 1.0);
+}