PAY ADMIN - Add manager/PO sign off mechanism

### UI features

Every fee change generates a change record
Change record includes:

- Before / after values
- Reason for change (required comment)
- Approval block (status, approver, date)

Fee cannot be re‑activated until the change record is approved

### How approval happens

Either:

- Manager signs off outside the tool (email / SharePoint / ticket)
- Or receives a lightweight review link (read-only view)

No files, tests, or entry points are named in the issue; start by locating the PAY ADMIN fee-change flow and any existing change-record handling. Done means recording before/after values, requiring a reason, tracking approval status, approver, and date, and preventing reactivation until approval is recorded, with either an external sign-off reference or a read-only review link.

Written by the indexing model from the issue text.