Fix --exec interactive prompt bug and create comprehensive test suite

Major fixes:
- Fixed --exec entering Python REPL instead of game loop
- Resolved screenshot transparency issue (requires timer callbacks)
- Added debug output to trace Python initialization

Test suite created:
- 13 comprehensive tests covering all Python-exposed methods
- Tests use timer callback pattern for proper game loop interaction
- Discovered multiple critical bugs and missing features

Critical bugs found:
- Grid class segfaults on instantiation (blocks all Grid functionality)
- Issue #78 confirmed: Middle mouse click sends 'C' keyboard event
- Entity property setters have argument parsing errors
- Sprite texture setter returns improper error
- keypressScene() segfaults on non-callable arguments

Documentation updates:
- Updated CLAUDE.md with testing guidelines and TDD practices
- Created test reports documenting all findings
- Updated ROADMAP.md with test results and new priorities

The Grid segfault is now the highest priority as it blocks all Grid-based functionality.

tests/ui_Grid_test_simple.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Simple test for mcrfpy.Grid"""
+import mcrfpy
+
+print("Starting Grid test...")
+
+# Create test scene
+print("[DEBUG] Creating scene...")
+mcrfpy.createScene("grid_test")
+print("[DEBUG] Setting scene...")
+mcrfpy.setScene("grid_test")
+print("[DEBUG] Getting UI...")
+ui = mcrfpy.sceneUI("grid_test")
+print("[DEBUG] UI retrieved")
+
+# Test grid creation
+try:
+    # Texture constructor: filename, sprite_width, sprite_height
+    # kenney_ice.png is 192x176, so 16x16 would give us 12x11 sprites
+    texture = mcrfpy.Texture("assets/kenney_ice.png", 16, 16)
+    print("[INFO] Texture created successfully")
+except Exception as e:
+    print(f"[FAIL] Texture creation failed: {e}")
+    exit(1)
+grid = None
+
+try:
+    # Try with just 2 args
+    grid = mcrfpy.Grid(20, 15)  # Just grid dimensions
+    print("[INFO] Grid created with 2 args")
+except Exception as e:
+    print(f"[FAIL] 2 args failed: {e}")
+    
+if not grid:
+    try:
+        # Try with 3 args  
+        grid = mcrfpy.Grid(20, 15, texture)
+        print("[INFO] Grid created with 3 args")
+    except Exception as e:
+        print(f"[FAIL] 3 args failed: {e}")
+
+# If we got here, add to UI
+try:
+    ui.append(grid)
+    print("[PASS] Grid created and added to UI successfully")
+except Exception as e:
+    print(f"[FAIL] Failed to add Grid to UI: {e}")
+    exit(1)
+
+# Test grid properties
+try:
+    print(f"Grid size: {grid.grid_size}")
+    print(f"Position: {grid.position}")
+    print(f"Size: {grid.size}")
+except Exception as e:
+    print(f"[FAIL] Property access failed: {e}")
+
+print("Test complete!")