Why: Keep the approved RDM export controls and the U3 material browser coverage in one component candidate.
Evidence: Changes in store.ts touch separate state fields and behavior; full Frontend tests/build and task-owned browser cases will be rerun after this merge.
Impact: Includes upstream RDM export UI without changing U3 source or notice contracts.
Refs: Dev U3 r0.4 Task 6 final review synchronization