feat(procedural): add plasma, voronoi, normalmap generators

Add three new procedural texture generators:
- gen_plasma: classic sine-sum color texture (RGB output)
- gen_voronoi: Worley cellular noise (F1/F2/F2-F1 modes)
- gen_normalmap: post-process grayscale→RGB normal map

Remove gen_noise_256 (was an alias for gen_noise). Register new
generators in asset_manager and asset_packer. Add unit tests for
all three, and use them in test_3d_render (plasma sky, voronoi noise,
fBm normal map).

handoff(Gemini): plasma/voronoi/normalmap procedural generators added;
gen_noise_256 removed; tests + 3d_render usage wired up.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/util/asset_manager.cc b/src/util/asset_manager.cc
index 0b96cb2..26a82bf 100644
--- a/src/util/asset_manager.cc
+++ b/src/util/asset_manager.cc
@@ -28,8 +28,10 @@ static const ProcGenEntry kAssetManagerProcGenFuncs[] = {
     {"gen_perlin", procedural::gen_perlin},
     {"gen_grid", procedural::gen_grid},
     {"make_periodic", procedural::make_periodic},
+    {"gen_plasma", procedural::gen_plasma},
+    {"gen_voronoi", procedural::gen_voronoi},
+    {"gen_normalmap", procedural::gen_normalmap},
 #if !defined(STRIP_ALL)
-    {"gen_noise_256", procedural::gen_noise_256},
     {"gen_fail", procedural::gen_fail},
 #endif
 };