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_cpu.h

@@ -0,0 +1,94 @@
+#pragma once
+
+#include "pxl8_atlas.h"
+#include "pxl8_colormap.h"
+#include "pxl8_math.h"
+#include "pxl8_mesh.h"
+#include "pxl8_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct pxl8_cpu_backend pxl8_cpu_backend;
+typedef struct pxl8_cpu_render_target pxl8_cpu_render_target;
+
+typedef struct pxl8_cpu_render_target_desc {
+    u32 width;
+    u32 height;
+    bool with_depth;
+    bool with_lighting;
+} pxl8_cpu_render_target_desc;
+
+typedef struct pxl8_3d_frame {
+    u8 ambient_light;
+    pxl8_vec3 camera_dir;
+    pxl8_vec3 camera_pos;
+    f32 far_clip;
+    u8 fog_color;
+    f32 fog_density;
+    f32 near_clip;
+    pxl8_mat4 projection;
+    f32 time;
+    pxl8_mat4 view;
+} pxl8_3d_frame;
+
+pxl8_cpu_backend* pxl8_cpu_create(u32 width, u32 height);
+void pxl8_cpu_destroy(pxl8_cpu_backend* cpu);
+
+void pxl8_cpu_begin_frame(pxl8_cpu_backend* cpu, const pxl8_3d_frame* frame);
+void pxl8_cpu_end_frame(pxl8_cpu_backend* cpu);
+
+void pxl8_cpu_clear(pxl8_cpu_backend* cpu, u8 color);
+void pxl8_cpu_clear_depth(pxl8_cpu_backend* cpu);
+
+void pxl8_cpu_set_colormap(pxl8_cpu_backend* cpu, const pxl8_colormap* cm);
+void pxl8_cpu_set_palette(pxl8_cpu_backend* cpu, const u32* palette);
+
+void pxl8_cpu_draw_pixel(pxl8_cpu_backend* cpu, i32 x, i32 y, u8 color);
+u8 pxl8_cpu_get_pixel(pxl8_cpu_backend* cpu, i32 x, i32 y);
+void pxl8_cpu_draw_line_2d(pxl8_cpu_backend* cpu, i32 x0, i32 y0, i32 x1, i32 y1, u8 color);
+void pxl8_cpu_draw_rect(pxl8_cpu_backend* cpu, i32 x, i32 y, i32 w, i32 h, u8 color);
+void pxl8_cpu_draw_rect_fill(pxl8_cpu_backend* cpu, i32 x, i32 y, i32 w, i32 h, u8 color);
+void pxl8_cpu_draw_circle(pxl8_cpu_backend* cpu, i32 cx, i32 cy, i32 radius, u8 color);
+void pxl8_cpu_draw_circle_fill(pxl8_cpu_backend* cpu, i32 cx, i32 cy, i32 radius, u8 color);
+void pxl8_cpu_draw_line_3d(pxl8_cpu_backend* cpu, pxl8_vec3 v0, pxl8_vec3 v1, u8 color);
+
+void pxl8_cpu_draw_mesh(
+    pxl8_cpu_backend* cpu,
+    const pxl8_mesh* mesh,
+    pxl8_mat4 model,
+    pxl8_material material,
+    const pxl8_atlas* textures
+);
+
+void pxl8_cpu_draw_mesh_wireframe(
+    pxl8_cpu_backend* cpu,
+    const pxl8_mesh* mesh,
+    pxl8_mat4 model,
+    u8 color
+);
+
+u8* pxl8_cpu_get_framebuffer(pxl8_cpu_backend* cpu);
+u32 pxl8_cpu_get_height(const pxl8_cpu_backend* cpu);
+u32 pxl8_cpu_get_width(const pxl8_cpu_backend* cpu);
+
+pxl8_cpu_render_target* pxl8_cpu_create_render_target(const pxl8_cpu_render_target_desc* desc);
+void pxl8_cpu_destroy_render_target(pxl8_cpu_render_target* target);
+
+pxl8_cpu_render_target* pxl8_cpu_get_target(pxl8_cpu_backend* cpu);
+void pxl8_cpu_set_target(pxl8_cpu_backend* cpu, pxl8_cpu_render_target* target);
+
+void pxl8_cpu_blit(pxl8_cpu_backend* cpu, pxl8_cpu_render_target* src, i32 x, i32 y, u8 transparent_idx);
+
+bool pxl8_cpu_push_target(pxl8_cpu_backend* cpu);
+void pxl8_cpu_pop_target(pxl8_cpu_backend* cpu);
+u32 pxl8_cpu_get_target_depth(const pxl8_cpu_backend* cpu);
+
+u8* pxl8_cpu_render_target_get_framebuffer(pxl8_cpu_render_target* target);
+u32 pxl8_cpu_render_target_get_height(const pxl8_cpu_render_target* target);
+u32 pxl8_cpu_render_target_get_width(const pxl8_cpu_render_target* target);
+
+#ifdef __cplusplus
+}
+#endif