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

src/pxl8_rng.c

@@ -1,24 +0,0 @@
-#include "pxl8_rng.h"
-
-void pxl8_rng_seed(pxl8_rng* rng, u32 seed) {
-    if (!rng) return;
-    rng->state = seed ? seed : 1;
-}
-
-u32 pxl8_rng_next(pxl8_rng* rng) {
-    if (!rng) return 0;
-    rng->state ^= rng->state << 13;
-    rng->state ^= rng->state >> 17;
-    rng->state ^= rng->state << 5;
-    return rng->state;
-}
-
-f32 pxl8_rng_f32(pxl8_rng* rng) {
-    return (f32)pxl8_rng_next(rng) / (f32)0xFFFFFFFF;
-}
-
-i32 pxl8_rng_range(pxl8_rng* rng, i32 min, i32 max) {
-    if (min >= max) return min;
-    u32 range = (u32)(max - min);
-    return min + (i32)(pxl8_rng_next(rng) % range);
-}