Implement `UI` and extension logic

[frixaco]

• Basic UI elements (buttons, actions, etc.)
• Manual two-way synchronization (buttons, requests)
• Improve loading state (authing, fetching, etc.)
• Manage Projects (requests)
• User login/registration (Github/Google/etc. vs email/password)
• Auto send changes (websockets)
• Integrate @vscode/webview-ui-toolkit