Issue #1: Settings Modal Implementation

### Description
Implement a comprehensive settings modal that allows users to configure their service credentials and customize their dashboard.

### Requirements
- [ ] Create a modal component with tabs for different services
- [ ] Add form validation for API keys and usernames
- [ ] Implement secure storage of credentials (localStorage with encryption)
- [ ] Add service connection status indicators
- [ ] Include "Test Connection" functionality for each service
- [ ] Add import/export settings functionality

### Acceptance Criteria
- Users can add/edit/remove service credentials
- Form validation prevents invalid inputs
- Settings are persisted across sessions
- Visual feedback for connection status
- Responsive design for mobile devices

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