CSV export shows raw cents instead of a formatted amount (#27)

[Param-Harrison]

Closes #27

Summary

The CSV export's amount column printed raw integer cents (4500) instead of a decimal amount (45.00). exportCsv in src/csv.ts now formats that column with formatCents, following the handling-money rule to format only at the output edge. The fix also applies to the CLI export command and to GET /api/groups/:id/export.csv, because both call exportCsv.

Acceptance criteria

AC	Evidence (command / test)	Result
AC-1	bun test tests/csv.test.ts: exportCsv > formats the amount column as a decimal via formatCents gives 45.00, 12.00, 30.00	pass
AC-2	bun test tests/csv.test.ts: exportCsv > keeps the header row and one line per expense	pass
AC-3	With src/csv.ts reverted to main, bun test tests/csv.test.ts fails (received ["1200","3000","4500"])	pass
AC-4	bun test tests/cli.test.ts tests/routes.test.ts: both export tests fail when the fix is reverted and pass with it (17 pass, 0 fail across csv/cli/routes)	pass
AC-5	make check: tsc --noEmit clean, bun test 29 pass / 0 fail, all 9 skills valid	pass

Non-goals respected

• NG-1: nothing under src/money/** changed. formatCents is reused as-is.
• NG-2: the CSV header, the column order and csvEscape are unchanged. Only how the amount field is written changed.
• NG-3: the JSON API (amountCents is still integer cents) and public/index.html are untouched.
• NG-4: src/routes/export.ts and src/cli.ts are untouched. The fix is only in src/csv.ts.
• NG-5: no protected paths were edited and there is no schema or DB change.

The test that bites

• Test: tests/csv.test.ts › exportCsv > formats the amount column as a decimal via formatCents
• Fails on main: git checkout main -- src/csv.ts, then bun test tests/csv.test.ts gives 1 pass, 1 fail (received "1200","3000","4500", expected "12.00","30.00","45.00")
• Passes here: bun test tests/csv.test.ts gives 2 pass, 0 fail

Gate line

FACTORY_GATES: status=GREEN passed=3 failed=0 skipped=1 failed_gates=audit

(audit was skipped. make audit is not part of make check.)

Protected paths touched

none

Reviewer findings addressed

none (the full evidence is in the factory verdict comment on #27)

Human checklist

• AC table has real evidence, not placeholders
• Non-goals respected
• Gate line is GREEN
• Protected paths are "none", or the change to them is expected and reviewed
• I ran the test that bites myself

🤖 Generated with Claude Code

[Param-Harrison]

/factory revise Add a test where the amount has a trailing zero cent, e.g. 45.50, so we know the column is not truncated.