fix(plugin-cloud-storage): prevent deleting original file when duplicating (#14961)

### What

Fixes the `beforeChange` hook in the `cloud-storage-plugin` to only
delete files from storage when the operation is `update`, not during
`create` (which includes duplication).

### Why

When duplicating a media document, the `previousDoc` parameter is
populated with the source document being duplicated. The existing
condition `if (previousDoc)` incorrectly triggered file deletion,
removing the original file from cloud storage (R2/S3/etc.) while the
original database document still referenced it.

This resulted in:
  - Original document in database with broken file reference
  - Original file deleted from cloud storage
  - New duplicated document working correctly

### How

- Added `operation` to the destructured hook parameters
- Changed the condition from `if (previousDoc)` to `if (previousDoc &&
operation === 'update')`
- Files are now only deleted when genuinely updating an existing
document with a new file, not when duplicating

Author: jhb-dev

packages/plugin-cloud-storage/src/hooks/afterChange.ts

@@ -11,15 +11,14 @@ interface Args {
 
 export const getAfterChangeHook =
   ({ adapter, collection }: Args): CollectionAfterChangeHook<FileData & TypeWithID> =>
-  async ({ doc, previousDoc, req }) => {
+  async ({ doc, operation, previousDoc, req }) => {
     try {
       const files = getIncomingFiles({ data: doc, req })
 
       if (files.length > 0) {
-        // If there is a previous doc,
-        // And we have new files,
-        // We need to delete the old files before uploading new
-        if (previousDoc) {
+        // If there is a previous doc, files and the operation is update,
+        // delete the old files before uploading the new ones.
+        if (previousDoc && operation === 'update') {
           let filesToDelete: string[] = []
 
           if (typeof previousDoc?.filename === 'string') {