Do frontend of exclude attending and remove dashboardNews

[nabramow]

Do the frontend for the exclude attending fix in both dashboard and events page under 'Discover Events'.

Closes #8893

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• There are no console warnings when running the app
• Added tests where relevant
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[github-actions]

📝 Release Notes

This PR should be included in the release notes.

Suggested release note:

Fixed duplicate event listings so events you are already attending or organizing no longer appear in Discover Events and community event suggestions

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: include
Reasoning: This fixes a noticeable duplicate-events issue in two user-facing event discovery areas: events users are already attending or organizing will no longer also appear in community/discover event lists. That is a meaningful UX improvement users will notice when browsing events. The dashboardNews removal is internal and not release-note worthy, but the event filtering change is.