fix: persist custom_prompt and replace autosave with save button

[Movm]

Summary

• Fix getProfile() to include custom_prompt in the returned profile data (was silently dropped on page reload)
• Replace unreliable autosave with an explicit Save button (btn-primary) for the custom prompt field
• Track dirty state so the button only appears when the prompt has unsaved changes
• Gitignore Remotion build output, bump tar override

Test plan

• Open profile, enter a custom prompt, click "Speichern" — confirm it persists after page reload
• Verify the Save button only appears when the prompt text differs from the saved value
• Confirm name/email/username fields still autosave as before