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/rules/zod-namespace-import.yml

@@ -0,0 +1,11 @@
+id: zod-namespace-import
+language: typescript
+severity: error
+message: Use namespace import for zod - `import * as z from "zod"` instead of named import
+note: |
+  Named imports from zod (e.g., `import { z } from "zod"`) should be replaced
+  with namespace imports (`import * as z from "zod"`) for consistency and to
+  ensure all zod utilities are available under the `z` namespace.
+rule:
+  pattern: import { $$$IMPORTS } from "zod"
+fix: import * as z from "zod";