Improve member's organizations sorting

[sausage-todd]

1. Those without dateEnd, but with dateStart should be at the top, orderd by dateStart
2. Those with dateEnd and dateStart should be in the middle, ordered by dateEnd
3. Those without dateEnd and dateStart should be at the bottom, ordered by name

Changes proposed ✍️

What

🤖 Generated by Copilot at ea0a6fc

Modified the sortMembers method of the MemberRepository class to use a new sorting logic for the members based on their membership dates. This change improves the member sorting in the frontend as requested in issue #123.
​

🤖 Generated by Copilot at ea0a6fc

sortMembers changed
New logic for membership
Autumn leaves falling

Why

How

🤖 Generated by Copilot at ea0a6fc

• Implement new sorting logic for members based on their membership dates (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.