Fix zod imports with ast-grep namespace import rule

Applied ast-grep rule to convert named zod imports to namespace imports
across the api-contract package for consistency.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.ast-grep/rule-tests/__snapshots__/zod-namespace-import-snapshot.yml

@@ -0,0 +1,20 @@
+id: zod-namespace-import
+snapshots:
+  ? |
+    import { z } from "zod";
+  : fixed: |
+      import * as z from "zod"
+    labels:
+    - source: import { z } from "zod";
+      style: primary
+      start: 0
+      end: 24
+  ? |
+    import { z, ZodError } from "zod";
+  : fixed: |
+      import * as z from "zod"
+    labels:
+    - source: import { z, ZodError } from "zod";
+      style: primary
+      start: 0
+      end: 34