Add helper for grouping creator activity feed entries by date

[Chucks1093]

Summary
The creator activity feed lists entries in chronological order without any date grouping, making it hard to find activity from a specific day. A grouping helper that inserts date headers between entries from different days improves scannability.

Scope

• add a helper that groups a list of activity feed entries by their date
• render a date header row between groups
• ensure the date headers are accessible to screen readers as section labels

Acceptance Criteria

• activity entries are visually grouped under their respective date headers
• the date headers are announced by screen readers when navigating the list
• the grouping does not affect the sort order of entries within a group

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg