refactor: clean upload pipeline and restore draco delivery

app/api/upload/check/route.ts

@@ -6,6 +6,7 @@ import { getModelFolderPath } from '@/lib/model-paths'
 import { ensurePreparedStagingAssets } from '@/lib/upload-staging'
 import { parseStagingRequestBody } from '@/lib/upload-request'
 import { getErrorMessage } from '@/lib/guards'
+import type { FileDiff } from '@/lib/types'
 
 export const runtime = 'nodejs'
 export const dynamic = 'force-dynamic'
@@ -37,7 +38,7 @@ export async function POST(req: NextRequest) {
       const remoteFileMap = new Map(files.map((file) => [file.name.toLowerCase(), file.size]))
       const { fileChanges, deletedFileNames } = classifyFileChanges(filesToPush, remoteFileMap, folderPath)
 
-      const diffs: Array<{ name: string; status: 'new' | 'changed' | 'deleted' }> = []
+      const diffs: FileDiff[] = []
 
       for (const [name, status] of fileChanges.entries()) {
         if (status === 'new' || status === 'changed') {