[Backend] User Financial Summary API

[Olowodarey]

📋 Description

Create comprehensive financial summary endpoint showing user's complete financial picture.

Acceptance Criteria

• GET /analytics/financial-summary for authenticated user
• Include: total savings, total interest earned, total deposits, total withdrawals
• Calculate savings rate and growth percentage
• Show allocation across different savings products
• Compare with previous periods (MoM, YoY)
• Include projected earnings for next 12 months
• Cache with 1-hour TTL

Tasks

• Create financial summary endpoint
• Implement calculations
• Add period comparisons
• Add projections
• Implement caching
• Write tests