feat: scripting system (C# or Lua)

[Hekbas]

Add a scripting layer to allow gameplay logic authoring without recompiling the engine.

Tasks

• Evaluate and choose runtime: Mono/.NET (C# scripting) vs. Lua (lightweight embedding)
• Integrate chosen runtime as a dependency
• Implement script component (Component::Script) with asset reference
• Expose engine API to scripts: entity manipulation, input, time, math
• Implement script lifecycle: OnCreate, OnUpdate, OnDestroy, OnCollision
• Hot-reload support (recompile/reload scripts without restarting the engine)
• Script editor integration (external IDE launch, or embedded code editor panel)
• Error handling and sandboxing (script errors should not crash the engine)