🛠️ [Feature]: Integrate actual databse with login.go

### What is the feature?

The login flow should authenticate users using credentials stored in the persistent database instead of mock or temporary data.

### Technical Implementation

_No response_

### Component(s) affected

- [ ] Coordination server
- [ ] Clientside Agent (WireGuard / NAT / CLI)
- [ ] Desktop client (Frontend)
- [ ] Docs / infra
- [ ] Other

### Alternatives considered

_No response_

Start with login.go and trace how the current mock or temporary credentials are checked. Identify the project's persistent database integration before changing the login flow. Done means authentication uses credentials stored in the persistent database instead of mock data, while the existing login flow continues to work.

Written by the indexing model from the issue text.