## Problem
On the dashboard **Net Worth Evolution** monthly bar chart, users with a
large negative net worth (lots of debt) saw an **empty chart** — only
the x-axis month labels rendered, no bars.
Root cause: the chart scales each asset segment so the stacked bar
height equals net worth. For negative net worth the scale factor was
clamped to zero:
```ts
const scaleFactor = hasLiabs && totalAssets > 0
? Math.max(0, netWorth / totalAssets) // negative net worth -> 0 -> every bar collapses
: 1;
```
A stack of positive asset segments simply can't represent a negative
total, so everything collapsed to zero height.
## Fix
- Extract the scaling into a tested pure helper
`computeNetWorthBarScaling`.
- When net worth is **negative**, hide the (meaningless) scaled asset
segments and draw the deficit as a **single downward bar** from a **zero
baseline** (dashed reference line).
- **Positive** periods still stack assets upward. Both directions round
only at their far end and meet the zero line flush, so upward and
downward bars look symmetric.
- Extend the same handling to the **daily area chart**, which shared the
bug through the same scaled dataset.
- Share a single `NetWorthMode` type across the bar/area charts and
tooltip (was duplicated in three places).
- Translate the tooltip **Net Worth / Total** labels (were hardcoded
English; added `Net Worth` to `lang/es.json`).
- Render the chart for **liability-only** users (a debtor with just a
loan) instead of the "No account data available" empty state.
## Tests
- Unit tests for `computeNetWorthBarScaling`: no-liabilities, positive,
negative-with-assets, liabilities-only, net-worth-exactly-zero, and
no-assets cases.
- `bun run test`, `prettier --check`, `eslint` all green on the touched
files.
## QA
Verified in the running app (Playwright) with two seeded users:
- **Heavily indebted** (net worth −56.250,00 €): the chart now renders
red downward bars instead of an empty area.
- **Net worth crossing zero**: negative months draw downward, positive
months stack upward, sharing the zero baseline; tooltip shows
per-account balances + the (now translated) "Patrimonio Neto" total.
## Demo
https://github.com/user-attachments/assets/7a9b167f-c037-4c82-8b68-f32932be99fe
## Screenshots
**Before** — empty chart, only x-axis labels:
<!-- PLACEHOLDER: before screenshot -->
<img width="1440" height="900" alt="net-worth-before"
src="https://github.com/user-attachments/assets/3bf9b3e3-ae75-4230-bca7-e7246a9a35d9"
/>
**After** — negative net worth as downward bars:
<img width="1440" height="900" alt="net-worth-after-tooltip"
src="https://github.com/user-attachments/assets/85302f0a-e427-4cbf-baba-5b1414049e9f"
/>
<img width="1440" height="900" alt="net-worth-after-mixed"
src="https://github.com/user-attachments/assets/41f08331-f055-4245-beeb-8d071c0d5d6d"
/>
<img width="1440" height="900" alt="net-worth-after-negative"
src="https://github.com/user-attachments/assets/c8610b03-dcff-46de-8987-d47c477ddd85"
/>
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