chore(deps): bump zod + react-hook-form (#7074)

bump zod - ref
trpc/trpc#7073 (review)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Upgraded Zod to v4 across the repo and updated related form/resolver
packages and typings.
  * Minor environment default adjusted (TYPEDOC).

* **Documentation**
* Added a new "zod v4" async-iterable validation example in
subscriptions docs.

* **Chores / Examples**
* Removed one experimental react-hook-form factory/example from the demo
app.

* **Notes**
* Tests and snapshots updated to reflect new validation error
formatting; no other user-facing behavior changes expected.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: KATT

package.json

@@ -54,7 +54,7 @@
     "superjson": "^1.12.4",
     "tsx": "^4.19.3",
     "ws": "^8.0.0",
-    "zod": "^3.25.51"
+    "zod": "^4.2.1"
   },
   "devDependencies": {
     "@playwright/test": "^1.50.1",