Use blueprint isOptional/isNullable for model property nullability

The blueprint now exposes `isOptional` and `isNullable` on properties. Map
them to the two orthogonal C# concepts instead of emitting every model
property as optional+nullable:

- DataMember IsRequired = !isOptional (payload presence)
- C# nullable annotation = isNullable (value may be null)

Endpoint parameters are unchanged (they carry isRequired). Bump
@seamapi/blueprint to ^0.60.0. The generated output is regenerated and
formatted by the Generate CI workflow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ThCbfBhJb4Hydvo8Es4qJA

Author: claude

codegen/lib/build-model.ts

@@ -158,10 +158,14 @@ const normalizeItemKind = (property: Property): Kind => {
 }
 
 const normalizeProperty = (property: Property): Field => {
-  // Resource properties do not carry required/nullable metadata; every model
-  // property is emitted as optional and nullable so response deserialization
-  // never fails on a missing or added field.
-  const base = { name: property.name, isRequired: false, nullable: true }
+  // `isOptional` controls whether the property must be present in the payload
+  // (the DataMember IsRequired flag); `isNullable` controls whether its value
+  // may be null (the C# nullable annotation). The two are independent.
+  const base = {
+    name: property.name,
+    isRequired: !property.isOptional,
+    nullable: property.isNullable,
+  }
   switch (property.format) {
     case 'string':
     case 'id':

package-lock.json

@@ -58,7 +58,7 @@
     "npm": ">=10.9.4"
   },
   "devDependencies": {
-    "@seamapi/blueprint": "^0.59.0",
+    "@seamapi/blueprint": "^0.60.0",
     "@seamapi/smith": "^0.5.2",
     "@seamapi/types": "1.970.0",
     "@types/node": "^24.10.9",