- Introduce Event variant and Overloaded helper for input handling
- Move game state (camera, client_world, dev_panel) from App to WorldScene
- Add SceneManager with push/pop/change operations for scene stack
- Refactor input callbacks to dispatch events through scene hierarchy
- Extract Argument struct to separate header
- Update Renderer and WorldRenderer to accept world reference
- Replace global input state with event-driven processing in ClientPlayer, Camera, etc.
Replace the old `Text` class with a new component-based UI system consisting of `Widget` and `Label` classes. Key changes:
- Remove `Text` class and its GPU upload logic; introduce `Label` as a `Widget` subclass with dirty-flag vertex update.
- Add `UIVertexData` struct to manage per-label vertex buffer/array and memory.
- Refactor `DebugCollector` to store labels in a `Widget` tree, removing hash-based lookup.
- Simplify `Font::vertices()` signature by removing position/scale parameters; scaling is now applied in the renderer’s model matrix.
- Update `Renderer` with `render_label()` and move UI rendering to a `render_ui()` that renders the widget tree.
- Add new source files `label.cpp`, `widget.cpp`, `ui_vertex_data.cpp` and update CMakeLists.
