feat(physics): Implement SDF-based physics engine and BVH

Completed Task #49.
- Implemented CPU-side SDF library (sphere, box, torus, plane).
- Implemented Dynamic BVH construction (rebuilt every frame).
- Implemented PhysicsSystem with semi-implicit Euler integration and collision resolution.
- Added visual debugging for BVH nodes.
- Created test_3d_physics interactive test and test_physics unit tests.
- Updated project docs and triaged new tasks.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/3d/visual_debug.cc b/src/3d/visual_debug.cc
index f8d9bed..ab4cb6c 100644
--- a/src/3d/visual_debug.cc
+++ b/src/3d/visual_debug.cc
@@ -182,6 +182,25 @@ void VisualDebug::add_box(const mat4& transform, const vec3& local_extent,
   }
 }
 
+void VisualDebug::add_aabb(const vec3& min, const vec3& max, const vec3& color) {
+  vec3 p[] = {{min.x, min.y, min.z}, {max.x, min.y, min.z}, {max.x, max.y, min.z},
+              {min.x, max.y, min.z}, {min.x, min.y, max.z}, {max.x, min.y, max.z},
+              {max.x, max.y, max.z}, {min.x, max.y, max.z}};
+
+  DebugLine edges[] = {
+      {p[0], p[1], color}, {p[1], p[2], color}, {p[2], p[3], color},
+      {p[3], p[0], color}, // Front
+      {p[4], p[5], color}, {p[5], p[6], color}, {p[6], p[7], color},
+      {p[7], p[4], color}, // Back
+      {p[0], p[4], color}, {p[1], p[5], color}, {p[2], p[6], color},
+      {p[3], p[7], color} // Connections
+  };
+
+  for (const auto& l : edges) {
+    lines_.push_back(l);
+  }
+}
+
 void VisualDebug::update_buffers(const mat4& view_proj) {
   // Update Uniforms
   wgpuQueueWriteBuffer(wgpuDeviceGetQueue(device_), uniform_buffer_, 0,