[DwC export]: Add Schema Mapper tool to User Tools

[grantfitzsimmons]

Goal

Add a Schema Mapper entry to the User Tools menu that opens a dialog listing all existing schemamapping records.

Background

Users currently have no dedicated UI for managing schema mappings. The new dialog must segment mappings into Core and Extension sections, providing a central place to create and manage them.

Acceptance Criteria

• "Schema Mapper" appears in the User Tools menu (Institution Admins only).
• Clicking it opens a dialog with two labeled sections: Core and Extension.
• Each section lists existing schemamapping records by name.
• Dialog has New and Close action buttons.
• No schemamapping records results in an empty state message per section.