Follow-up to #644: Extract duplicate get_home_dir() implementations
into a single pub fn in config.rs, reducing code duplication across
codex_config.rs, gemini_config.rs, and settings.rs.
Also adds documentation comments to build.rs explaining the Windows
manifest workaround for test binaries.
- Format all TypeScript/React code with Prettier
- Format all Rust code with cargo fmt
- Fix bundle identifier from .app to .desktop to avoid macOS conflicts
- Prepare codebase for v3.0.0 Tauri release