Add spinner overlay when creating/opening a project to prevent double-click crash

[markusfurtlehner]

Problem

Double-pressing the create or open project button crashes the backend. There is no loading indicator to signal that the operation is in progress, so users can accidentally trigger the action twice.

Expected behavior

• Show a spinner overlay when create/open project is clicked
• Disable further interaction until the operation completes
• Prevent duplicate requests that crash the backend

Steps to reproduce

1. Click "Create Project" or "Open Project"
2. Quickly click the button again before the operation finishes
3. Backend crashes

Proposed solution

• Add a spinner/loading overlay on the project creation/opening UI
• Disable the button (or the entire dialog) while the request is in flight
• Optionally debounce or guard the backend endpoint against concurrent duplicate requests