## What
Between visits, highlight the transactions that arrived since the user
last opened the list.
- The newest `created_at` from the initial page load is stored in
`localStorage` (`transactions-last-visit`), frozen at mount.
- Every transaction whose `created_at` is newer than that marker gets a
subtle accent on the row (left border + faint tint).
## Why per-row instead of a single divider line
The first cut drew one "Last visit" divider with new rows above it. A
code review found this is structurally wrong: the list is sorted by
`transaction_date` (when the money moved), but "new" is defined by
`created_at` (when the row was inserted). The two don't correlate — a
bank sync that imports a batch dated across several days scatters the
new rows throughout the list, so a single boundary lands at the first
older row and **hides every new row below it**, the exact miss the
feature was meant to prevent.
Per-row marking is correct regardless of sort order: no new transaction
can be hidden.
## Notes / limitations
- The marker is written **once at mount** from the initial payload. Rows
that arrive mid-visit (load-more, a sync/refresh, AI categorization) do
not advance it, so they are never recorded as "seen" before the user has
seen them. The trade-off is they may re-appear as new next visit (errs
on showing, never hiding).
- Purely client-side (localStorage), so the marker is per-device.
## Tests
- Unit tests for `isNewSince` and `newestCreatedAt`.
- `LocalizationTest`, ESLint, Prettier all pass.
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