feat(gameplay): implement entity movement system with collision detection

- Add Velocity and HitBoxes components to entity
- Introduce HitboxManager for loading per-entity collision AABBs from JSON
- Create MoveSystem with per-axis collision handling
- Move get_block_aabb to base World class and add virtual get_per_tick_time
- Remove static get_block_aabb from ClientWorld; use member m_per_tick_time for tick duration

src/CMakeLists.txt

@@ -96,4 +96,6 @@ target_sources(${PROJECT_NAME}
         render/model_manager.cpp
         render/model_renderer.cpp
         gameplay/chunk.cpp
+        gameplay/move_system.cpp
+        gameplay/hitbox_manager.cpp
 )