Update organizations default sorter

[joanagmaia]

Changes proposed ✍️

What

🤖 Generated by Copilot at 1cd1dc8

Changed the default sorting criteria of the organization members table from joinedAt to activityCount in frontend/src/modules/organization/store/state.js. This makes the table more informative and relevant to the issue #123.
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🤖 Generated by Copilot at 1cd1dc8

activityCount
now sorts organization
falling leaves of work

Why

How

🤖 Generated by Copilot at 1cd1dc8

• Sort organization members by activity count instead of join date (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.