CSV export shows raw cents instead of a formatted amount

[Param-Harrison]

What happened

The amount column in the CSV export (and the CLI's export command,
which shares the same code) prints the raw integer cents, e.g. 1000,
instead of a formatted decimal amount like 10.00.

Expected

The amount column should read 10.00, matching the money formatting
convention used everywhere else (the web page, the balances output).

Steps to reproduce

curl -s http://localhost:3200/api/groups/flat-4b/export.csv -H "Authorization: Bearer flat-priya"

or

bun run src/cli.ts export flat-4b

Look at the amount column: values like 4500, 1200, 3000 instead of
45.00, 12.00, 30.00.

Area

export

Severity

low

Notes for whoever picks this up

src/csv.ts's exportCsv builds the row with r.amountCents directly.
It should use formatCents from src/money/cents.ts (see the
handling-money skill: "format only at the edge").