fix: replace SHA comparison with file size for LFS compatibility + add NoChangesModal

Git LFS stores pointer files whose SHA differs from the actual blob SHA,
causing false-positive diffs on every upload. Switching to file size
comparison resolves this for LFS-enabled repos.

Also replaces the inline error message with a dedicated NoChangesModal
when no differences are detected, offering cancel (reset) or modify
(close modal) actions.

lib/types.ts

@@ -18,7 +18,7 @@ export interface FileDiff {
 
 export interface RemoteFile {
   name: string
-  sha: string
+  size: number
 }
 
 export type UploadResponse =