feat(core): add terrain shaping parameters

core/include/vf/Terrain.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <cstdint>
+#include "World.h"
+
+namespace vf {
+
+struct TerrainParams {
+    uint32_t seed = 1337u;
+    int chunksX = 8;
+    int chunksZ = 8;
+    int worldHeight = 64;   // in blocks
+    int seaLevel = 26;
+    int baseHeight = 24;
+    float amplitude = 18.0f;
+    float frequency = 0.015f;  // world-space sample scale
+    int octaves = 5;
+    bool trees = true;
+};
+
+// Fills `world` with a bounded heightmap terrain: stone core, dirt, grass,
+// sand near water, water up to sea level, snow on peaks, and scattered trees.
+void generateTerrain(World& world, const TerrainParams& params);
+
+// Terrain surface height (topmost solid block y) for a world column.
+int columnHeight(uint32_t seed, const TerrainParams& params, int gx, int gz);
+
+} // namespace vf