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/asset/pxl8_save.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "pxl8_types.h"
+
+#define PXL8_SAVE_MAX_SLOTS 10
+#define PXL8_SAVE_HOTRELOAD_SLOT 255
+#define PXL8_SAVE_MAX_PATH 512
+
+typedef struct pxl8_save pxl8_save;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+pxl8_save* pxl8_save_create(const char* game_name, u32 magic, u32 version);
+void pxl8_save_destroy(pxl8_save* save);
+
+pxl8_result pxl8_save_delete(pxl8_save* save, u8 slot);
+bool pxl8_save_exists(pxl8_save* save, u8 slot);
+void pxl8_save_free(u8* data);
+const char* pxl8_save_get_directory(pxl8_save* save);
+pxl8_result pxl8_save_read(pxl8_save* save, u8 slot, u8** data_out, u32* size_out);
+pxl8_result pxl8_save_write(pxl8_save* save, u8 slot, const u8* data, u32 size);
+
+#ifdef __cplusplus
+}
+#endif