#52 fix: enforce membership check before deleting/updating shared brain

[kstij]

Summary

This PR fixes an authorization bypass vulnerability that allowed any user to delete or update a shared brain by setting isShare: true and providing the brain's ID without verifying membership.

Vulnerability Details

Previously, the deleteBrain function did not confirm that the requesting user was a member of the shared brain. This allowed unauthorized users to perform destructive actions on shared resources.

Fix

• Added a membership check when isShare is true:
  • Queries ShareBrain for a matching record of the brain and user.
  • Throws an unauthorized error if no match is found.
  • Proceeds with deletion/update only for authorized members.

[Jay-Thesia-Weam]

@kstij Deleting the archive brain permanently (Hard delete), we only remove it from brain table,
we have to also remove it from sharebrain and ChatMember table, Add this enhancement after that do the PR again.

[kstij]

Enhancement Complete: Added proper cleanup of related records when permanently deleting brains

Changes made:

• Added cleanup of ShareBrain records when permanently deleting a brain
• Added cleanup of ChatMember records when permanently deleting a brain
• Imported ChatMember model in brain service
• Added error handling for cleanup operations
• Enhanced both single brain deletion and bulk deletion
• Maintained backward compatibility for soft deletes

What this fixes:

• Prevents orphaned ShareBrain records when brains are permanently deleted
• Prevents orphaned ChatMember records when brains are permanently deleted
• Ensures data consistency across the database
• Addresses the moderator's feedback about proper cleanup