Keep an Audit Trail on Timesheets

A client queried an invoice and I could not prove the hours had not been changed. Build me a timesheet audit trail. Record every creation, edit and deletion of a time entry with the person who made the change, the date and time, the original value, the new value and, for any change to already-approved time, a mandatory reason. Never overwrite an original value; keep it alongside the change. Once a period is approved and exported, lock it so corrections must be made as clearly marked adjustments in a later period rather than by altering history. Let me see the full history of any entry, and search changes by person, period or reason. Add an AI agent that reviews editing activity and flags unusual patterns such as time entered long after the work, entries repeatedly edited upward before invoicing, or a single person making many retrospective changes, presenting these as things to look at rather than as accusations. Automate two things: an alert on any change to approved time, and a scheduled monthly report of retrospective changes. Two logins: a user who sees their own history, and an owner who sees all changes.