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/simple_timer_screenshot_test.py

@@ -30,7 +30,7 @@ mcrfpy.setScene("test")
 ui = mcrfpy.sceneUI("test")
 
 # Add visible content - a white frame on default background
-frame = mcrfpy.Frame(100, 100, 200, 200,
+frame = mcrfpy.Frame(pos=(100, 100), size=(200, 200),
                     fill_color=mcrfpy.Color(255, 255, 255))
 ui.append(frame)