Fix joined on custom platform

[gaspergrom]

Changes proposed ✍️

What

🤖 Generated by Copilot at b34bfc8

Simplify and fix platform display logic for dashboard members. The file dashboard-members.vue is updated to handle null values and remove an extra condition for showing the last activity platform of dashboard members.
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🤖 Generated by Copilot at b34bfc8

getPlatformDetails
Simpler and more robust now
Autumn bugs swept away

Why

How

🤖 Generated by Copilot at b34bfc8

• Simplify and fix the logic for displaying the member's last activity platform in the dashboard (link, link)
• Remove the unnecessary condition that checks if the platform is valid in frontend/src/modules/dashboard/components/dashboard-members.vue (link)
• Add optional chaining and nullish coalescing operators to the platform name expression in the same file (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.