Improve request workflow

[f0reachARR]

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[gemini-code-assist]

Code Review

This pull request enhances the university request approval process by allowing administrators to choose between creating a new organization or attaching the request to an existing one. The changes span database migrations, API schema updates, and frontend UI improvements to support this dual-mode workflow. Additionally, the PR introduces email notifications for approved participation requests. A critical issue was identified in the backend logic where the check for existing pending invitations uses the representative's email, while the actual invitation is issued to the requester's email, potentially allowing duplicate invitations.