## Problem
When an income category contained both incoming and outgoing
transactions (e.g. an \"Income from Rents\" category that also holds
property-related expense payments), the Sankey endpoint was summing
**all** amounts together and applying `abs()` to the net result.
Real example reported:
| Date | Description | Amount |
|------|-------------|--------|
| Mar 13 | BIZUM sent — Lavadora | -€124.03 |
| Mar 10 | BIZUM received — luz febrero | +€38.04 |
| Mar 9 | Endesa energy payment | -€38.04 |
| Mar 4 | BIZUM received — agua Febrero | +€41.34 |
| Mar 2 | Comunidad de Propietarios | -€105.92 |
- Net: **-€188.61** → `abs()` → **€188.61 shown as income** ❌
- Correct: sum of positive flows only → **€79.38** ✅
## Fix
Added a sign filter to `getCategoryBreakdown()` before the `GROUP BY`
aggregation:
- Income categories: `WHERE transactions.amount > 0`
- Expense categories: `WHERE transactions.amount < 0`
This ensures the Sankey shows the **actual gross flow** on each side
rather than a misleading abs-of-net.
## Test
Added a regression test in `CashflowAnalyticsTest` that reproduces the
exact five transactions from the reported scenario and asserts the
Sankey returns `7938` cents (€79.38) instead of the buggy `18861`
(€188.61).
9e2a9cadfe