refactor: tighten upload and viewer contracts

lib/github.ts

@@ -202,7 +202,8 @@ async function uploadToLfsBatch(
     throw new Error(`LFS batch request failed (${batchRes.status}): ${text}`)
   }
 
-  const batchObjects = parseLfsBatchResponse(await batchRes.json())
+  const batchData: unknown = await batchRes.json()
+  const batchObjects = parseLfsBatchResponse(batchData)
 
   const objectMap = new Map(objects.map((o) => [o.oid, o]))
 
@@ -277,7 +278,7 @@ export async function getRemoteFolder(
     })
 
     if (!Array.isArray(data)) {
-      return { exists: false, files: [] }
+      throw new Error(`Le chemin distant ${folderPath} existe mais ce n'est pas un dossier`)
     }
 
     const files: RemoteFile[] = await Promise.all(