docs(normalization): illustrate worked examples with dj.Diagram figures

src/explanation/normalization.md

@@ -215,6 +215,8 @@ class MouseWeight(dj.Manual):
     """
 ```
 
+![Fully normalized mouse-housing schema, left to right: Mouse and Cage as entity tables; CageAssignment and MouseWeight as event tables keyed by date, each depending on Mouse. CageAssignment references Cage as a secondary (dashed) foreign key.](../images/norm-mouse-housing.svg)
+
 This fully normalized design:
 
 - **Intrinsic attributes only** — `Mouse` contains only attributes determined at creation (birth date, sex)
@@ -299,6 +301,8 @@ class Delivery(dj.Manual):
     """
 ```
 
+![Workflow-normalized order schema, left to right: Order (referencing Product and Customer as secondary, dashed foreign keys), then a one-to-one chain Order → Payment → Shipment → Delivery, each step a separate table.](../images/norm-order-workflow.svg)
+
 The foreign keys now form a chain — `Order → Payment → Shipment → Delivery` —
 that is simultaneously the referential-integrity structure and the workflow
 diagram. Every attribute is non-nullable, because a row exists only once its step