Phase 2 backend complete - Full CRUD for shipping methods.
New Endpoints:
✅ GET /methods/available - List all available shipping methods
✅ POST /zones/{id}/methods - Add method to zone
✅ DELETE /zones/{id}/methods/{instance_id} - Remove method
✅ GET /zones/{id}/methods/{instance_id}/settings - Get method form fields
✅ PUT /zones/{id}/methods/{instance_id}/settings - Update method settings
Features:
- Get available methods (Flat Rate, Free Shipping, etc.)
- Add any method to any zone
- Delete methods from zones
- Fetch method settings with current values
- Update method settings (cost, conditions, etc.)
- Proper error handling
- Cache clearing after changes
Next: Frontend implementation
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