fix: Improve add users to org (calcom#25314)

* Improve add users to org

* Improve add users to org

* test: Add comprehensive tests for handleUserEvents cross-tenant hijack prevention

- Add tests for cross-tenant hijack prevention security fix
- Test that users belonging to different organizations are blocked
- Test that users with null organizationId are blocked (prevents legacy user hijacking)
- Test that users belonging to correct organization succeed
- Test new user creation flow
- Test user activation/deactivation flows
- Test custom attribute syncing
- All 8 tests passing locally with proper type safety (no 'as any' usage)

Co-Authored-By: Volnei Munhoz <volnei.munhoz@gmail.com>

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: volnei