Add comprehensive tests for session cleanup and async CRUD operations; improve error handling and validation across schemas and API routes

- Introduced extensive tests for session cleanup, async session CRUD methods, and concurrent cleanup to ensure reliability and efficiency.
- Enhanced `schemas/users.py` with reusable password strength validation logic.
- Improved error handling in `admin.py` routes by replacing `detail` with `message` for consistency and readability.

backend/app/alembic/versions/1174fffbe3e4_add_performance_indexes.py

@@ -0,0 +1,78 @@
+"""add_performance_indexes
+
+Revision ID: 1174fffbe3e4
+Revises: fbf6318a8a36
+Create Date: 2025-11-01 04:15:25.367010
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = '1174fffbe3e4'
+down_revision: Union[str, None] = 'fbf6318a8a36'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Add performance indexes for optimized queries."""
+
+    # Index for session cleanup queries
+    # Optimizes: DELETE WHERE is_active = FALSE AND expires_at < now AND created_at < cutoff
+    op.create_index(
+        'ix_user_sessions_cleanup',
+        'user_sessions',
+        ['is_active', 'expires_at', 'created_at'],
+        unique=False,
+        postgresql_where=sa.text('is_active = false')
+    )
+
+    # Index for user search queries (basic trigram support without pg_trgm extension)
+    # Optimizes: WHERE email ILIKE '%search%' OR first_name ILIKE '%search%'
+    # Note: For better performance, consider enabling pg_trgm extension
+    op.create_index(
+        'ix_users_email_lower',
+        'users',
+        [sa.text('LOWER(email)')],
+        unique=False,
+        postgresql_where=sa.text('deleted_at IS NULL')
+    )
+
+    op.create_index(
+        'ix_users_first_name_lower',
+        'users',
+        [sa.text('LOWER(first_name)')],
+        unique=False,
+        postgresql_where=sa.text('deleted_at IS NULL')
+    )
+
+    op.create_index(
+        'ix_users_last_name_lower',
+        'users',
+        [sa.text('LOWER(last_name)')],
+        unique=False,
+        postgresql_where=sa.text('deleted_at IS NULL')
+    )
+
+    # Index for organization search
+    op.create_index(
+        'ix_organizations_name_lower',
+        'organizations',
+        [sa.text('LOWER(name)')],
+        unique=False
+    )
+
+
+def downgrade() -> None:
+    """Remove performance indexes."""
+
+    # Drop indexes in reverse order
+    op.drop_index('ix_organizations_name_lower', table_name='organizations')
+    op.drop_index('ix_users_last_name_lower', table_name='users')
+    op.drop_index('ix_users_first_name_lower', table_name='users')
+    op.drop_index('ix_users_email_lower', table_name='users')
+    op.drop_index('ix_user_sessions_cleanup', table_name='user_sessions')