Bugfix/app freeze

[preet-bhadra]

[!IMPORTANT] Fix app freeze by correcting SettingsModal import and improving modal state management in Header.tsx and SettingsModal.tsx.

• Header.tsx:
  • Fix import: Rename SettingsCard to SettingsModal.
  • Add state isSettingsModalOpen to manage SettingsModal visibility.
  • Replace SettingsCard with a button to toggle SettingsModal.
• SettingsModal.tsx:
  • Remove unused imports and useDisclosure hook.
  • Add SettingsModalProps interface for props.
  • Use activeTab state to toggle between 'appearance' and 'api-keys' tabs.
  • Simplify modal rendering by removing unnecessary fragments and components.

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