[Formulus] Fix: Settings Screen Login Button State

[najuna-brian]

Problem

UX issue: The login button remained gray/disabled when returning to the Settings screen while already logged in.
Closes #141

Solution

• Added as const assertions to style properties in Alert button configurations to fix TypeScript type inference
• Added initialUsername and initialPassword state tracking alongside existing initialServerUrl
• Login button is now disabled (grey) when:
  • User is already logged in AND
  • Credentials (server URL, username, password) haven't changed from saved values
• Login button is enabled (green) when:
  • Not logged in, OR
  • Any credential field has been modified

Changes

• formulus/src/screens/SettingsScreen.tsx

Testing

1. Log in with valid credentials → navigates to home
2. Return to Settings screen → login button should be grey/disabled
3. Modify any field (server URL, username, or password) → button turns green/enabled
4. Revert changes back to original → button turns grey/disabled again

[r0ssing]

Thanks for looking into this! Hmm.. are we sure we want the check for hasCredentialsChanged? I think that the button should still be active even when there are no changes (eg. when the auth token has expired, but the creds are the same) ❓

[najuna-brian]

Good point! I've removed the hasCredentialsChanged check ☺️

[r0ssing]

Looks great! I will test it manually asap! 😄