chore: export dropdown base component

[lawreka]

Summary

need to reuse the DropdownMenu and friends, this version with base-ui is the best one we have

Test Plan

• no visible changes

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Note

Low Risk
Low risk: this PR only changes component exports/types and doesn’t modify runtime behavior or data/auth flows. Main risk is minor API surface/typing changes affecting downstream imports.

Overview
Makes the code-group dropdown primitives reusable by exporting DropdownMenu, DropdownMenuTrigger, DropdownMenuContent, and DropdownMenuItem from code-group/index.ts.

Also exports the associated prop types (DropdownMenuProps, DropdownMenuTriggerProps, DropdownMenuContentProps, DropdownMenuItemProps) from dropdown.tsx and re-exports them through the code-group barrel for external consumption.

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