feat: enhance space management with admin controls and user permissions

- Remove member management UI, add admin-only dashboard
- Add user search by email and add to space functionality
- Implement space members table with permission management
- Add permission editing with checkboxes (read/write/delete/admin)
- Add space deletion capability for admins with confirmation dialog
- Ensure at least one permission is always selected per user
- Ensure at least one admin exists per space
- Add API functions: searchUserByEmail, getSpaceUsers, updateUserPermissionInSpace, deleteSpace
- Add visual indicators and tooltips for disabled permissions
- Include confirmation dialog requiring space name typing before deletion

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: kanekoshoyu