Add initial implementation of GeelectronDemo app

- Created main.js for the application logic, including tests for Electron app properties and methods.
- Added package.json to define app metadata.
- Included necessary code signature files for macOS app distribution.
- Implemented basic window management and event handling in the app.

crates/gelectron-app/Cargo.toml

@@ -17,3 +17,4 @@ log = { workspace = true }
 env_logger = { workspace = true }
 wry = "0.47"
 tao = "0.30"
+muda = "0.15"