examples: add with-zod-form-action

[Vish05]

What?

Adds a new example (examples/with-zod-form-action) demonstrating React 19's useActionState combined with Zod validation via the zod-form-action package.

Why?

Validating useActionState forms with Zod currently means repeating the same safeParse() / flatten().fieldErrors boilerplate in every Server Action, and it's easy to get subtle things wrong — like accidentally swallowing a redirect() call inside a try/catch, or silently dropping cross-field (object-level .refine()) validation errors. This example demonstrates a working pattern that handles both cases correctly, alongside standard field-level validation.

How?

The example is a standard create-next-app (App Router) project that includes:

• A Server Action using zodAction() for schema validation
• A client form reading typed field errors and form-level errors via fieldError() / formError()
• A redirect() call on successful submission, verified to fire correctly (not swallowed by internal error handling) after validation passes

Tested locally with npm run dev — field validation, form-level (cross-field) validation, and the post-success redirect were all confirmed working.

N/A — this PR adds a new example, not a documentation fix, bug fix, or new feature, so the corresponding checklists above don't apply.

Signed commits: commits are SSH-signed (git config gpg.format ssh).

Closes NEXT-
Fixes #