Fix wxChoice/wxComboBox dropdown rendering and add tests

- Fix empty clip region bug in wx.js clipRect function
- Add dropdown mouse interaction tests
- Add *.log to gitignore
- Make build script clean by default (use --no-clean to skip)
- Add wxGLCanvas canvas element fix documentation

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

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

.gitignore

@@ -39,3 +39,4 @@ wxwidgets-clean/
 /tests/wasm-app/*.js
 /tests/wasm-app/minimal_test.wasm
 /temp/
+*.log