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>

tools/ludic-cli/prelude.ludic

@@ -35,6 +35,22 @@ function write_file(path: pointer, s: pointer) -> bool {
   return true
 }
 
+# ---- byte strings ------------------------------------------------------------------
+# s[a, b) as a fresh NUL-terminated string; out-of-range ends are clamped.
+function str_sub(s: pointer, a: int, b: int) -> pointer {
+  var lo = a
+  if lo < 0 { lo = 0 }
+  var hi = b
+  if hi < lo { hi = lo }
+  let out = bytes(hi - lo + 1)
+  var i = lo
+  var k = 0
+  while i < hi { out[k] = s[i];  k += 1;  i += 1 }
+  out[k] = 0
+  return out
+}
+function str_space(c: int) -> bool { return c == 32 or c == 9 or c == 13 }
+
 function file_exists(path: pointer) -> bool { return shq(`test -e {path}`) }
 function is_exec(path: pointer) -> bool { return shq(`test -x {path}`) }
 # is `a` newer than `b` (like the shell's `-nt`)?