[TASK-2026-02-03-BACKEND-ENTITIES-SYNC] feat: Create backend services for new DDL tables
Services created:
- education/instructor.service.ts: CRUD for education.instructors
- education/tag.service.ts: Course tags and assignments management
- trading/drawing.service.ts: Chart drawing tools persistence
- ml/prediction-overlay.service.ts: ML prediction overlays CRUD
- payments/refund.service.ts: Stripe refund workflow management
Types added:
- Instructor, CourseTag, CourseTagAssignment interfaces
- DrawingTool, DrawingTemplate, DrawingToolType types
- PredictionOverlay, OverlayType, OverlayStyleConfig
- Refund, RefundStatus, RefundRow interfaces
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>