refactor: Rename click property to on_click (closes #139)

Breaking change: callback property standardized to on_* pattern.
- `drawable.click` → `drawable.on_click`

Updated all C++ bindings (8 files) and Python test usages.
Note: src/scripts changes tracked separately (in .gitignore).

This establishes the naming pattern for future callbacks:
on_click, on_enter, on_exit, on_move, on_key, etc.

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

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

tests/unit/WORKING_automation_test_example.py

@@ -68,7 +68,7 @@ frame.children.append(caption)
 def frame_clicked(x, y, button):
     print(f"Frame clicked at ({x}, {y}) with button {button}")
 
-frame.click = frame_clicked
+frame.on_click = frame_clicked
 
 print("Scene setup complete. Setting timer for automation tests...")
 

tests/unit/ui_Frame_test_detailed.py

@@ -67,7 +67,7 @@ def test_issue_42_click_callback():
     try:
         frame1 = mcrfpy.Frame(10, 10, 200, 150)
         ui.append(frame1)
-        frame1.click = correct_callback
+        frame1.on_click = correct_callback
         print("✓ Click callback with correct signature assigned successfully")
     except Exception as e:
         print(f"✗ Failed to assign correct callback: {type(e).__name__}: {e}")
@@ -80,7 +80,7 @@ def test_issue_42_click_callback():
     try:
         frame2 = mcrfpy.Frame(220, 10, 200, 150)
         ui.append(frame2)
-        frame2.click = wrong_callback_no_args
+        frame2.on_click = wrong_callback_no_args
         print("✓ Click callback with no args assigned (will fail at runtime per issue #42)")
     except Exception as e:
         print(f"✗ Failed to assign callback: {type(e).__name__}: {e}")
@@ -93,7 +93,7 @@ def test_issue_42_click_callback():
     try:
         frame3 = mcrfpy.Frame(10, 170, 200, 150)
         ui.append(frame3)
-        frame3.click = wrong_callback_few_args
+        frame3.on_click = wrong_callback_few_args
         print("✓ Click callback with 2 args assigned (will fail at runtime per issue #42)")
     except Exception as e:
         print(f"✗ Failed to assign callback: {type(e).__name__}: {e}")