fix(randomUUID): add fallback when crypto.randomUUID is unavailable (HTTP/older envs)

In some environments (non-secure origins like http, older browsers, certain test runners),
`crypto.randomUUID` is not available, causing runtime errors.

This change preserves the existing fast path when `crypto.randomUUID` exists, and adds a
RFC4122 v4-shaped fallback for other cases:

- Detects availability via: typeof crypto !== 'undefined' && crypto.randomUUID
- Uses `crypto.randomUUID.bind(crypto)` when present
- Otherwise formats a UUID using 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(...)
  with Math.random, ensuring version (4) and variant (8|9|a|b) bits
- Keeps strict typing with template-literal UUID type for DX

No breaking changes.

Author: ziyak97

packages/agents-core/src/shims/shims-browser.ts

@@ -82,7 +82,14 @@ export class BrowserEventEmitter<
 
 export { BrowserEventEmitter as RuntimeEventEmitter };
 
-export const randomUUID = crypto.randomUUID.bind(crypto);
+export const randomUUID: () => `${string}-${string}-${string}-${string}-${string}` =
+  (typeof crypto !== 'undefined' && crypto.randomUUID)
+    ? crypto.randomUUID.bind(crypto)
+    : () => 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
+      const r = Math.random() * 16 | 0;
+      const v = c === 'x' ? r : (r & 0x3 | 0x8);
+      return v.toString(16);
+    }) as `${string}-${string}-${string}-${string}-${string}`;
 export const Readable = class Readable {
   constructor() {}
   pipeTo(