## What
Clicking a parent category in the cashflow **Money Flow** Sankey now
expands its children inline as an extra column branching off the parent
— expenses grow to the right, income to the left — instead of swapping
the whole chart for a drilled-in view.
<img width="782" height="392" alt="image"
src="https://github.com/user-attachments/assets/6ce7d925-19d2-4744-a5da-6884a9583a4d"
/>
## Behaviour
- Toggle: click a parent to expand, click again to collapse. Multiple
parents can be open at once.
- One level deep (a child with its own children is not further
expandable).
- The parent stays as an intermediate node and its flow splits into the
children + a node for transactions booked directly on the parent
(labelled **Parent**).
- Changing the period resets expansions.
## Implementation
- `sankey-chart.tsx`: dynamic column layout (was fixed 3-column); lazily
fetches children via the existing `/api/cashflow/sankey?parent=`
endpoint and caches them; label + amount now render in a `foreignObject`
so flexbox handles spacing, vertical centering, and CSS-ellipsis
truncation (full name kept in a `title`); expand affordance is a
`ChevronsRight` icon.
- Child nodes use the same `MIN_NODE_HEIGHT` and gap as top-level nodes,
centered on the parent so links fan out cleanly.
- Removed the old drill-replace + breadcrumb flow (and the now-unused
`sankeyParent` hook option).
- Backend: the direct-transactions node is renamed from `"<name>
(direct)"` to `"Parent"` (+ `es` translation).
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