refactor(setup): replace skills selection with auto-install progress UI
- Replace manual skill bundle selection with automatic installation step
- Add InstallingContent component with real-time progress feedback
- Auto-install essential components: OpenCode, Python, Code Assist, File Tools, Terminal
- Show animated progress bar and per-skill installation status
- Auto-proceed to completion after installation finishes
- Update CompleteContent to display installed components
- Update architecture docs and build process documentation
