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>

runtime/native/input.ludic

@@ -223,6 +223,9 @@ var in_mx0: int = 0       # x/y at the previous frame (for the delta)
 var in_my0: int = 0
 var in_mdx: int = 0       # delta this frame
 var in_mdy: int = 0
+var in_rdx: int = 0       # the raw motion the platform reports while captured
+var in_rdy: int = 0
+var in_cursor_mode: int = 0
 var in_mbtn: int = 0      # button bitmask (bit 0 left, 1 right, 2 middle)
 var in_wheel: int = 0     # wheel delta this frame
 # gamepads: connected flag, button bitmask, and IN_AXES fixed axes each
@@ -298,9 +301,11 @@ function input_device_commit(k: int, replaying: int) -> void {
     # headless, from the single polled key. Injection (in_sim) is OR-ed on top.
     if is_windowed() {
       win_held(in_dev)
-      let mbuf = words(4)                              # [x, y, button-mask, wheel]
+      let mbuf = words(6)                              # [x, y, button-mask, wheel, raw dx, raw dy]
+      mbuf[4] = 0;  mbuf[5] = 0
       win_mouse(mbuf)
       in_mx = mbuf[0];  in_my = mbuf[1];  in_mbtn = mbuf[2];  in_wheel = mbuf[3]
+      in_rdx = mbuf[4];  in_rdy = mbuf[5]
       # #51 — feed the platform gamepad + touch state into the same buffers the
       # read APIs use. Each is windowed-only glue (win_pad / win_touch are DCE'd
       # in a headless build); on hardware they overwrite the injected state.
@@ -334,6 +339,8 @@ function input_device_commit(k: int, replaying: int) -> void {
   # platform above when windowed, by Input.set_mouse before this poll otherwise).
   in_mdx = in_mx - in_mx0
   in_mdy = in_my - in_my0
+  # captured (mode 2): the cursor is a clamped reticle, the motion is the raw delta
+  if is_windowed() and in_cursor_mode == 2 { in_mdx = in_rdx;  in_mdy = in_rdy }
   in_mx0 = in_mx
   in_my0 = in_my
 }
@@ -438,6 +445,7 @@ enum CursorMode { Normal, Hidden, Locked, Confined }   # Input.cursor_mode(mode:
 enum PadButton { A, B, X, Y, LeftShoulder, RightShoulder, Back, Start }   # Input.bind_pad(button:) / pad_button
 enum MouseButton { Left, Right, Middle }                                  # Input.mouse_down(button:)
 function input_cursor_mode(mode: int) -> void {
+  in_cursor_mode = mode
   if is_windowed() { win_cursor_mode(mode) }
 }