Build fix: resolve duplicate React import in multi-select component (Mail & Vendor)

A build-breaking error was corrected by removing a duplicate React import from the multi-select dropdown component shared by the Mail and Vendor apps. This is a code-hygiene fix that unblocks builds; it changes no features or behavior.

The multiple-selector.tsx component in both the Mail and Vendor apps had a redundant import { forwardRef, useEffect } from "react" line that duplicated identifiers already imported at the top of the file. This duplicate-identifier error caused the compilation/build to fail, blocking deployments until it was removed.

No user-visible or functional change. The multi-select dropdown behaves exactly as before. The benefit is internal: the build pipeline compiles successfully again, allowing the Mail and Vendor apps to be built and promoted without errors.

• Removed a single duplicate line, import { forwardRef, useEffect } from "react";, from apps/mail/src/components/ui/multiple-selector.tsx.
• Removed the identical duplicate line from apps/vendor/src/components/ui/multiple-selector.tsx.
• Net change: 2 files modified, 0 additions, 2 deletions. The forwardRef and useEffect identifiers remain available via the existing import block at the top of each file.

Very low. The removed line was a redundant duplicate of existing imports, so no symbols are lost and no runtime logic is touched. The only realistic risk is a missed reference, which is mitigated by a successful build/compile (the failure this fix resolves) confirming both files still resolve all identifiers.

• Confirm the Mail and Vendor apps build/compile cleanly with no duplicate-identifier or unresolved-import errors.
• Smoke-test any screen that uses the multi-select dropdown in both apps: open it, type to filter, select and deselect multiple options.
• Verify no console errors related to forwardRef or useEffect on those screens.