Sort contact list by role then alphabetically in transaction tool

**Description:**
In the transaction tool's contact list, sort contacts by role first (admins before non-admins, separated by a visual divider), then alphabetically within each group.

**Acceptance Tests:**
- Admins appear before non-admins in the contact list
- A visual separator (e.g. divider or spacing) distinguishes the two groups
- Contacts within each group are sorted alphabetically