feat(engine): implement perspective FOV, pathfinding, and GUI text widgets

Major Engine Enhancements:
- Complete FOV (Field of View) system with perspective rendering
  - UIGrid.perspective property for entity-based visibility
  - Three-layer overlay colors (unexplored, explored, visible)
  - Per-entity visibility state tracking
  - Perfect knowledge updates only for explored areas

- Advanced Pathfinding Integration
  - A* pathfinding implementation in UIGrid
  - Entity.path_to() method for direct pathfinding
  - Dijkstra maps for multi-target pathfinding
  - Path caching for performance optimization

- GUI Text Input Widgets
  - TextInputWidget class with cursor, selection, scrolling
  - Improved widget with proper text rendering and input handling
  - Example showcase of multiple text input fields
  - Foundation for in-game console and chat systems

- Performance & Architecture Improvements
  - PyTexture copy operations optimized
  - GameEngine update cycle refined
  - UIEntity property handling enhanced
  - UITestScene modernized

Test Suite:
- Interactive visibility demos showing FOV in action
- Pathfinding comparison (A* vs Dijkstra)
- Debug utilities for visibility and empty path handling
- Sizzle reel demo combining pathfinding and vision
- Multiple text input test scenarios

This commit brings McRogueFace closer to a complete roguelike engine
with essential features like line-of-sight, intelligent pathfinding,
and interactive text input capabilities.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/UITestScene.cpp

@@ -121,7 +121,7 @@ UITestScene::UITestScene(GameEngine* g) : Scene(g)
     //UIEntity test:
     // asdf
     // TODO - reimplement UISprite style rendering within UIEntity class. Entities don't have a screen pixel position, they have a grid position, and grid sets zoom when rendering them.
-    auto e5a = std::make_shared<UIEntity>(*e5); // this basic constructor sucks: sprite position + zoom are irrelevant for UIEntity.
+    auto e5a = std::make_shared<UIEntity>(); // Default constructor - lazy initialization
     e5a->grid = e5;
     //auto e5as = UISprite(indextex, 85, sf::Vector2f(0, 0), 1.0);
     //e5a->sprite = e5as; // will copy constructor even exist for UISprite...?