feat(summary): Smart Weekly Digest — GET /summary/weekly (Issue #121)

[XavierAbraham]

Summary

Closes #121 — implements the Smart Weekly Digest feature with a new GET /summary/weekly endpoint.

What's included

packages/backend/app/routes/summary.py (new)

• GET /summary/weekly?weeks_back=N — returns a structured financial digest for the authenticated user
• Aggregation: total expenses, income, net cash flow, transaction counts
• Category breakdown: per-category spending sorted by amount desc
• Daily trend: 7-day sparkline data (all days filled, zeros where no data)
• Insights: auto-generated text comparing current vs previous week (% change, cash flow direction)
• Clean separation of pure functions (_aggregate_week, _category_breakdown, _daily_trend, _generate_insights) for testability

packages/backend/tests/test_summary.py (new)

• 10 unit tests across all helper functions
• Mocked DB — no live DB required
• Covers edge cases: empty weeks, first-week-ever, positive/negative cash flow

packages/backend/app/routes/__init__.py (updated)

• Registered summary_bp at /summary

API Response shape

{
  "period": { "start": "2026-03-16", "end": "2026-03-22", "label": "Week of Mar 16, 2026" },
  "summary": { "total_expenses": 150.0, "total_income": 500.0, "net": 350.0, "expense_count": 5, "income_count": 2 },
  "previous_week": { "total_expenses": 120.0, ... },
  "category_breakdown": [{ "category": "Food", "amount": 80.0, "count": 3 }],
  "daily_trend": [{ "date": "2026-03-16", "amount": 0.0 }, ...],
  "insights": ["Total spending increased by 25.0% vs last week (120.00 → 150.00).", "Positive cash flow this week: +350.00."]
}

Testing

cd packages/backend
pytest tests/test_summary.py -v

Authored-by: Xavier Abraham Sandoval abrahamsandoval.as@gmail.com