Rename Sorting Criteria in DRep Directory from "Activity" to "Voting Activity"

[bosko-m]

Update the label of the sorting criteria currently named "Activity" in the DRep Directory to "Voting Activity" to better reflect what is being measured and make the meaning clearer for users.

Acceptance Criteria

• Sorting option labeled "Activity" is renamed to "Voting Activity" across all instances in the DRep Directory UI.
• No changes to the underlying sorting logic or data.
• Confirm that the new label is shown consistently