The onSubmit handler was setting the datetime-local input's value to an
ISO UTC string (e.g. "2026-03-11T17:00:00.000Z"). datetime-local inputs
only accept the format "YYYY-MM-DDTHH:MM" — values with a 'Z' timezone
suffix are invalid and the browser silently clears the field to "". This
caused the form to submit an empty scheduledAt, which the server treated
as null, so games were always saved without a date.
Fix by keeping the datetime-local input for user interaction (renamed
scheduledAtLocal, not submitted) and writing the converted UTC ISO string
into a separate hidden input named scheduledAt in the onSubmit handler.
Also adds app/lib/date-utils.ts with a localDateTimeToUtcIso helper and
matching tests to document and verify the datetime-local ↔ ISO conversion
behaviour.
https://claude.ai/code/session_0148fgZiXpyvGX8ZX3BFRGCs
