## Summary
Adds a **category-analysis drawer** so you can see how much you spend on
a single category, month by month, over the last 12 months — answering
"am I spending more or less on food delivery?".
Reachable via an **Analyze** button on three cards:
- Dashboard → Top spending categories
- Cashflow → Income Sources
- Cashflow → Expense Categories
Each button opens a shared drawer with a full-width category chooser
(all categories) and a 12-month stacked bar chart.
## Chart semantics
- X = last 12 rolling months (gaps filled with zero). Y = user display
currency.
- Stacked segments = the chosen category's immediate children
(grandchildren rolled in) + a **Direct** segment (spend on the parent
itself) + an **Other** segment (children beyond the top 6, ranked by
total).
- A leaf category renders a single series named after the category.
- Amounts convert to the user currency and **net per month**, oriented
by category type so the expected direction reads as a positive bar; an
against-grain month (e.g. refunds > spend) dips below zero.
- Colors use the theme-aware chart palette (same as the net-worth
chart).
## Summary stats
Two glowing cards above the chart: **Monthly average** and **Trend**
(recent 6-month average vs earlier 6-month average; null when there's no
earlier baseline).
## Persistence
Each widget remembers its own chosen category in `localStorage`
(category only), prefilling the first category of its list otherwise; a
remembered-but-deleted category falls back gracefully.
## Tests
- 11 Pest feature tests (rollup, Direct/Other, net-with-refunds,
12-month window, currency conversion, income orientation, summary
average + trend).
- 5 vitest tests for the prefill/persistence precedence.
- es.json keys added.
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