feat(core): add A*-style mob pathfinding over the voxel grid

core/include/vf/Pathfind.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <vector>
+#include "World.h"
+#include "Math.h"
+
+namespace vf {
+
+struct PathConfig {
+    int mobHeight = 2;       // vertical voxels the walker occupies
+    int maxStepUp = 1;       // how high a single step can climb
+    int maxDrop = 3;         // how far a single step can fall
+    int maxExpansions = 40000;   // A* node budget before giving up
+};
+
+// A cell is standable when the walker's body fits (non-solid) and there is solid
+// ground directly beneath it.
+bool isStandable(const World& world, const Vec3i& cell, const PathConfig& config = {});
+
+// A* over standable voxel cells. Returns the cell path from start to goal
+// inclusive, or an empty path when the goal is unreachable, not standable, or the
+// search exceeds the node budget. Deterministic: ties break on a fixed ordering.
+std::vector<Vec3i> findPath(const World& world, const Vec3i& start, const Vec3i& goal,
+                            const PathConfig& config = {});
+
+} // namespace vf