refactor: reorganize pxl8 into client/src/ module structure

- core/: main entry, types, logging, I/O, RNG
- asset/: ase loader, cart, save, embed
- gfx/: graphics, animation, atlas, fonts, tilemap, transitions
- sfx/: audio
- script/: lua/fennel runtime, REPL
- hal/: platform abstraction (SDL3)
- world/: BSP, world, procedural gen
- math/: math utilities
- game/: GUI, replay
- lua/: Lua API modules

client/src/gfx/pxl8_gfx3d.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include "pxl8_3d_camera.h"
+#include "pxl8_math.h"
+#include "pxl8_mesh.h"
+#include "pxl8_types.h"
+
+typedef struct pxl8_gfx pxl8_gfx;
+
+typedef struct pxl8_3d_uniforms {
+    u8 ambient;
+    u8 fog_color;
+    f32 fog_density;
+    f32 time;
+} pxl8_3d_uniforms;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void pxl8_3d_begin_frame(pxl8_gfx* gfx, const pxl8_3d_camera* camera, const pxl8_3d_uniforms* uniforms);
+void pxl8_3d_clear(pxl8_gfx* gfx, u8 color);
+void pxl8_3d_clear_depth(pxl8_gfx* gfx);
+void pxl8_3d_draw_line(pxl8_gfx* gfx, pxl8_vec3 v0, pxl8_vec3 v1, u8 color);
+void pxl8_3d_draw_mesh(pxl8_gfx* gfx, const pxl8_mesh* mesh, pxl8_mat4 model, pxl8_material material);
+void pxl8_3d_draw_mesh_wireframe(pxl8_gfx* gfx, const pxl8_mesh* mesh, pxl8_mat4 model, u8 color);
+void pxl8_3d_end_frame(pxl8_gfx* gfx);
+u8* pxl8_3d_get_framebuffer(pxl8_gfx* gfx);
+const pxl8_frustum* pxl8_3d_get_frustum(pxl8_gfx* gfx);
+
+#ifdef __cplusplus
+}
+#endif