feat(durable-iterator): x-orpc-durable-iterator header (#1032)

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

- New Features
- Standardized the Durable Iterator response header to
x-orpc-durable-iterator for clearer interoperability.

- Documentation
- Added CORS guidance and examples showing how to expose the
x-orpc-durable-iterator header in server-side setup.

- Refactor
- Renamed the public Durable Iterator header; update any references to
the previous header name.

- Chores
- Minor internal alignment to reflect the new header name across the
integration.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: unnoq

apps/content/docs/integrations/durable-iterator.md

@@ -198,6 +198,22 @@ const handler = new RPCHandler(router, {
 })
 ```
 
+::: warning CORS Policy
+The `DurableIteratorHandlerPlugin` adds an `x-orpc-durable-iterator` header to responses, indicating that the response contains a durable iterator. For cross-origin requests, you must configure CORS to expose this header to clients.
+
+```ts
+const handler = new RPCHandler(router, {
+  plugins: [
+    new CORSPlugin({
+      exposeHeaders: ['x-orpc-durable-iterator'], // [!code highlight]
+    }),
+    new DurableIteratorHandlerPlugin(),
+  ],
+})
+```
+
+:::
+
 ## Client Side
 
 On the client side, simply configure the plugin. Usage is identical to [Event Iterator](/docs/client/event-iterator). The `url` in `DurableIteratorLinkPlugin` points to your Durable Object upgrade endpoint:

packages/durable-iterator/src/consts.ts

@@ -1,4 +1,4 @@
 export const DURABLE_ITERATOR_TOKEN_PARAM = 'token' as const
 export const DURABLE_ITERATOR_ID_PARAM = 'id' as const
-export const DURABLE_ITERATOR_PLUGIN_HEADER_KEY = 'x-orpc-dei' as const
+export const DURABLE_ITERATOR_PLUGIN_HEADER_KEY = 'x-orpc-durable-iterator' as const
 export const DURABLE_ITERATOR_PLUGIN_HEADER_VALUE = '1' as const