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>

changes/gl-render3d.md

@@ -0,0 +1,28 @@
+bump: minor
+type: feat
+**OpenGL for Ludic, and a 3D renderer on it.** `Gl.*` binds the whole OpenGL 4.1
+core API — every `gl*` entry point of the platform `gl3.h` as `Gl.<snake_name>(…)`
+with every `GL_*` constant, generated by `ludic-dev glgen` with per-call ABI thunks
+(`runtime/native/gl_thunks.ll`; float/double parameters take `fixed`). Windowed
+builds get an `NSOpenGLContext` on the existing window at Retina resolution
+(`cocoa.ll`); headless builds render into an offscreen CGL context, so a program
+that uses `Gl.*` renders and screenshots identically under the test harness.
+`Gl.open / swap / screenshot / program / vao / floats …` cover the glue, and the
+IEEE-float helpers (`f_add`, `mem_put_f32`, …) let Q16.16 programs fill real
+float vertex and uniform data. `Gl.*` links `gl.ll + gl_thunks.ll + OpenGL.framework`
+only when used; every other build is byte-identical.
+
+The `ludic.render3d` package (`packages/ludic.render3d`) is a physically based
+renderer written on `Gl.*`: HDRI sky with image-based lighting (irradiance, GGX
+prefiltered, split-sum BRDF, sun extracted from the map), GPU-generated terrain
+with scanned PBR materials (stochastic anti-tiling, triplanar rock, slope/altitude
+splatting), cascaded shadow maps with PCF and world-unit biasing, a glTF loader
+for scanned models, instanced vegetation with baked impostors, procedural grass
+and lupines with wind and translucency, 4x MSAA with alpha-to-coverage, SSAO,
+still water, cloud shadows, aerial perspective, an HDR pipeline with bloom,
+auto-exposure, ACES tonemapping, grading, sharpening and grain. See
+`examples/rendering/smooth.ludic`, and the Maroon Lake game (git.workshopsoft.io/workshopsoft/maroon-lake) for a
+game built on it. The renderer's CC0 materials are fetched with `ludic assets`.
+
+**16-bit PNGs**: the renderer's texture loader keeps 16-bit samples (normal /
+displacement maps) and uploads them as `RGB16` / `R16`.