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/zod-namespace-import-test.yml

@@ -0,0 +1,13 @@
+id: zod-namespace-import
+valid:
+  - |
+    import * as z from "zod";
+  - |
+    import * as z from "zod";
+    const schema = z.object({ name: z.string() });
+
+invalid:
+  - |
+    import { z } from "zod";
+  - |
+    import { z, ZodError } from "zod";