docs(sdk/react-native): align upload-files with UploadFileRequest API

Rewrite the React Native "Upload Files" guide to the request-object upload
API the RN SDK actually ships (CometChat.createUploadFileRequest ->
UploadFileRequest), mirroring the JS SDK guide (PR #427) section-for-section.
The previous draft documented a functional CometChat.uploadFiles() surface
that does not exist in @cometchat/chat-sdk-react-native.

- upload-files.mdx: createUploadFileRequest + UploadFileRequest, caller-
  supplied fileId, UploadFileListener.onFileProgress, UploadResult.batchId,
  getAttachments/getAttachmentsByType/getStatus (IN_PROGRESS/IDLE),
  addUploadListener, removeAttachment, clearAll, getMaxAttachmentCount().
  Retry documented as re-upload of the same fileId (RN has no
  retryAttachment()); RN-specific error codes added (ERR_UNAUTHENTICATED,
  ERR_PRESIGN_REJECTED, ERR_PRESIGN_FETCH_FAILED).
- send-message.mdx: fix phantom-API references — getFileUploadLimits() ->
  getMaxAttachmentCount(), uploadFiles() -> UploadFileRequest.
- docs.json: add the upload-files page to RN Messaging nav.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: suraj-chauhan-cometchat

docs.json

@@ -3521,6 +3521,7 @@
                             "group": "Messaging",
                             "pages": [
                               "sdk/react-native/send-message",
+                              "sdk/react-native/upload-files",
                               "sdk/react-native/receive-messages",
                               "sdk/react-native/additional-message-filtering",
                               "sdk/react-native/retrieve-conversations",

sdk/react-native/send-message.mdx

@@ -437,10 +437,16 @@ mediaMessage.setQuotedMessageId(10);
 
 ## Multiple Attachments in a Media Message
 
-Starting version 3.0.9 & above, the SDK supports sending multiple attachments in a single media message. There are two ways:
+Starting version 3.0.9 & above, the SDK supports sending multiple attachments in a single media message. A media message can carry up to a configurable maximum number of attachments (default **10**, controlled by the `file.count.max` app setting). `sendMediaMessage()` rejects with `ERR_FILE_COUNT_EXCEEDED` if you exceed it — read the current limit at runtime with `CometChat.getMaxAttachmentCount()`.
 
-1. **By providing an array of files** — Pass an array of file objects and CometChat uploads them automatically.
-2. **By providing URLs** — Use the [`Attachment`](/sdk/reference/auxiliary#attachment) class with multiple URLs.
+<Tip>
+**Recommended: upload first, then send.** For a real composer — where you want a progress bar per file, and the ability to remove or retry individual files — upload the files through an [`UploadFileRequest`](/sdk/react-native/upload-files), collect the resulting `Attachment`s, and attach them here with `setAttachments()`. This decouples the (slow, cancellable) upload from the (instant) send. See [Upload Files & Send Attachments](/sdk/react-native/upload-files) for the full flow.
+</Tip>
+
+There are two ways:
+
+1. **By providing an array of files** — Pass an array of file objects and CometChat uploads them automatically. This is the simplest path, but it gives no upload progress and no per-file cancel/retry — for that, [upload first](/sdk/react-native/upload-files).
+2. **By providing URLs** — Use the [`Attachment`](/sdk/reference/auxiliary#attachment) class with multiple URLs. This is also the path the [upload-then-send flow](/sdk/react-native/upload-files) uses — the `Attachment`s from an `UploadFileRequest` are ready to pass straight to `setAttachments()`.
 
 ### Upload Multiple Files