[Backend] User Entity & Secrets Ownership Model (#608 Phase 1-2) #870

Parent Issue

Part of #608 - User-Centric Session Tracking

Scope

Implement backend foundation for user entities and secrets ownership model.

Tasks

Phase 1: User Entity Management

• Create User entity type in knowledge graph
• Add user_id field to existing entities
• Implement user registration/login tracking
• Database migration for user entities

Phase 2: Secrets Ownership Model

• Add owner_id to Secret entities
• Implement scope levels (user, session, shared)
• Add session_id for session-scoped secrets
• Add shared_with field for explicitly shared secrets
• Implement encryption at rest
• Database migration for secrets model

Files to Modify

• autobot-user-backend/knowledge/entities.py
• autobot-user-backend/knowledge/graph.py
• autobot-user-backend/api/secrets.py
• autobot-shared/database/models/ (new models)

Acceptance Criteria

• User entity type exists in knowledge graph
• Secrets have owner_id, scope, session_id fields
• Secrets encrypted at rest
• Database migrations run successfully
• Unit tests pass

Dependencies

None - can start immediately

Labels

backend, database, knowledge-graph