Fix merging of members through Actions button

[skwowet]

Changes proposed ✍️

What

🤖 Generated by Copilot at 20fb479

Updated handleMergeMembers function to work with v-data-table component. Refactored member-list component to use Vuetify's v-data-table for better performance and usability.
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🤖 Generated by Copilot at 20fb479

selectedMembers
Cutting old selectedRows
Autumn of refactor

Why

How

🤖 Generated by Copilot at 20fb479

• Updated the handleMergeMembers function to use the selectedMembers computed property instead of the selectedRows data property (link)

Checklist ✅

• Label appropriately with Feature, Improvement, or Bug.
• Add screehshots to the PR description for relevant FE changes
• New backend functionality has been unit-tested.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.