Spending trend heatmap visualization

[rohitdash08]

Visualize spending intensity across time.

Acceptance Criteria

• Production ready implementation
• Includes tests
• Documentation updated

[Pranjal6955]

@rohitdash08 Can u assign this issue to me

[alexchenai]

/attempt #116

Implementing spending trend heatmap visualization. Service aggregates EXPENSE transactions into a day-of-week x ISO-week grid with pace statistics, day summaries, and busiest/quietest day identification. PR incoming.

[mendarb]

/attempt #116

Implementation Plan

Full-stack spending trend heatmap:

Backend (Flask):

• New GET /api/expenses/heatmap endpoint
• Aggregates daily spending totals over the last 12 months
• Returns data structured for calendar heatmap (date → amount)

Frontend (React):

• New SpendingHeatmap component using a calendar heatmap grid
• Color intensity based on spending amount (green → red scale)
• Tooltip showing date + exact amount on hover
• Responsive layout, integrates into Analytics page

Tests: Backend API tests + frontend component tests
Docs: Update API docs and component README

[alexchenai]

/attempt