Drove src/lib/csv.ts to 100% stmts/branch/funcs/lines (was 97.95%/55.55%):
- added a null-fallback row test covering every ?? default (activityName,
userName, insoleType→Kurk, pairCount→2, duration/paused→0) and the null
end-time branch (line 65).
- added CSV-escaping edge tests: commas, embedded quotes, and newlines inside
a field stay inside the quoted cell.
- added formatDuration edge (hours >99 → 100:00:00).
- added a /api/export ordering-by-start-time behavior test and adopted
resetDb per-test isolation in the export suite.
No bugs found; CSV code behaves correctly. sessions.ts /api/export route
already at 100%. Full api suite green (150 tests).
