feat(physics): add voltex_physics crate with Collider and ContactPoint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/voltex_physics/src/collider.rs

@@ -0,0 +1,42 @@
+use voltex_math::{Vec3, AABB};
+
+#[derive(Debug, Clone, Copy)]
+pub enum Collider {
+    Sphere { radius: f32 },
+    Box { half_extents: Vec3 },
+}
+
+impl Collider {
+    pub fn aabb(&self, position: Vec3) -> AABB {
+        match self {
+            Collider::Sphere { radius } => {
+                let r = Vec3::new(*radius, *radius, *radius);
+                AABB::new(position - r, position + r)
+            }
+            Collider::Box { half_extents } => {
+                AABB::new(position - *half_extents, position + *half_extents)
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sphere_aabb() {
+        let c = Collider::Sphere { radius: 2.0 };
+        let aabb = c.aabb(Vec3::new(1.0, 0.0, 0.0));
+        assert_eq!(aabb.min, Vec3::new(-1.0, -2.0, -2.0));
+        assert_eq!(aabb.max, Vec3::new(3.0, 2.0, 2.0));
+    }
+
+    #[test]
+    fn test_box_aabb() {
+        let c = Collider::Box { half_extents: Vec3::new(1.0, 2.0, 3.0) };
+        let aabb = c.aabb(Vec3::ZERO);
+        assert_eq!(aabb.min, Vec3::new(-1.0, -2.0, -3.0));
+        assert_eq!(aabb.max, Vec3::new(1.0, 2.0, 3.0));
+    }
+}