fix: Update test files to use current API patterns

Migrates test suite to current API:
- Frame(x, y, w, h) → Frame(pos=(x, y), size=(w, h))
- Caption("text", x, y) → Caption(pos=(x, y), text="text")
- caption.size → caption.font_size
- Entity(x, y, ...) → Entity((x, y), ...)
- Grid(w, h, ...) → Grid(grid_size=(w, h), ...)
- cell.color → ColorLayer system

Tests now serve as valid API usage examples.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/unit/test_pathfinding_integration.py

@@ -21,10 +21,8 @@ for i in range(5):
     grid.at(5, i + 2).walkable = False
 
 # Create entities
-e1 = mcrfpy.Entity(2, 5)
-e2 = mcrfpy.Entity(8, 5)
-grid.entities.append(e1)
-grid.entities.append(e2)
+e1 = mcrfpy.Entity((2, 5), grid=grid)
+e2 = mcrfpy.Entity((8, 5), grid=grid)
 
 # Test pathfinding between entities
 print(f"Entity 1 at ({e1.x}, {e1.y})")