[FE-061] Create canonical frontend architecture doc mapping app/data layers

[Topmatrixmor2014]

This pull request addresses issue #892 by creating comprehensive frontend architecture documentation that maps the application and data layers for the Stellar Earn frontend application.

Changes Made:

• Added docs/FRONTEND_ARCHITECTURE.md with detailed documentation
• High-level architecture overview with layer breakdown
• Detailed mapping of presentation, application, state management, and data access layers
• Component organization and domain mapping
• Data flow patterns (read, write, real-time, optimistic updates)
• Security architecture and authentication flow
• Performance optimization strategies
• Testing architecture guidelines
• Best practices for component design, state management, and API integration

Closes #892

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