fix: activity history group headers render as "Invalid date"

[everysingletear]

Problem

In the activity timeline (UserActivities), every group header renders as "Invalid date" for most locales.

groupByDate builds its grouping key with toLocaleDateString():

const date = new Date(item.performedAt || item.updatedAt).toLocaleDateString()

and the timeline then renders that same key back through the localized formatter:

{fmt.date(date)}

fmt.date hands the string to moment, which cannot reparse a locale-formatted date — "16.07.2026", "2026/7/16", "16/07/2026" are all unparseable. The result is a literal Invalid date where the day heading should be.

It happens to look fine only where the locale format is close enough to a format moment guesses correctly, which is why it is easy to miss on an en-US dev machine.

Fix

Key the groups on a stable local ISO day (YYYY-MM-DD) — a format fmt.date parses reliably — instead of a display string. Records with no usable timestamp go into an unknown bucket rendered as an em dash, so a missing performedAt/updatedAt no longer produces Invalid date either.

Built the key from local date parts rather than toISOString() on purpose: toISOString() converts to UTC and would shift activity into the wrong day for anyone east or west of UTC around midnight.

Notes

• Group ordering is unchanged. The keys are non-integer strings, so object insertion order is preserved exactly as before — groups still follow the order records arrive in.
• No string/i18n changes; this is purely the grouping key.
• Single file, 14 lines. Build is green.