Refactor code into modular structure and add comprehensive tests

- Split main.rs into 10 focused modules for better maintainability
- Add 37 unit tests covering desktop entry, Tauri config, validation,
  Chromium backend, and app config serialization
- Update version to v0.1.1-alpha.1

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "deskify"
-version = "0.1.0"
+version = "0.1.1-alpha.1"
 edition = "2024"
 
 [dependencies]