feat: context management CRUD — create, update, deprecate, merge entities

[rajnavakoti]

Description

Today there are no CRUD operations for managing the knowledge base. Entities are created by extraction and that's it. Need lifecycle operations: create manually, update/enrich, deprecate, merge duplicates, link to sources.

Acceptance Criteria

• Create entity manually (via CLI or UI)
• Update entity content/relationships
• Deprecate entity (soft delete with reason)
• Merge duplicate entities
• All operations produce an audit trail (who changed what, when)
• UI interface for curation workflow

Out of Scope

• Multi-user collaboration
• Approval workflows
• Version control integration (git handles this)