feat(demo): migrate demo to new ECS implementation

[Copilot]

The demo application was using the deprecated class-based ECS architecture. Updated all demo files to use the new interface-based, data-oriented ECS system introduced in this PR.

Migration Changes

• Components: Converted from classes extending Component to interfaces with symbol-based IDs via createComponentId
• Systems: Converted from classes extending System to factory functions returning { query, run } objects
• Entity building: Changed from world.buildAndAddEntity([...components]) to world.createEntity() + world.addComponent(entity, componentId, data)
• Camera setup: Replaced registerCamera() helper with manual camera entity creation using cameraId component
• Input setup: Replaced registerInputs() with direct InputManager instantiation and explicit system registration

Example

Before (class-based):

export class MoveSystem extends System {
  constructor(time: Time) {
    super([PositionComponent, MoveComponent], 'MoveSystem');
    this._time = time;
  }
  
  public run(entity: Entity): void {
    const pos = entity.getComponentRequired(PositionComponent);
    const move = entity.getComponentRequired(MoveComponent);
    // ...
  }
}

world.addSystem(new MoveSystem(time));

After (factory function):

export const createMoveEcsSystem = (
  time: Time,
): EcsSystem<[PositionEcsComponent, MoveEcsComponent]> => ({
  query: [positionId, moveId],
  run: (result) => {
    const [pos, move] = result.components;
    // ...
  },
});

world.addSystem(createMoveEcsSystem(time));

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