Files & Sizes explorer: browse Depot & Workspace as a tree with per-file/folder weight

- Backend depot_ls (p4 dirs + p4 sizes -s recursive summary per child + p4 sizes for direct files) and fs_ls (local recursive folder sizing), both confined
- Tools -> Files & Sizes: Depot/Workspace tabs, lazy-loading tree, size bars, heaviest-first sort, folder file counts, open-in-explorer
- humanSize() helper + FsEntry type; i18n in 5 languages

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/Cargo.lock

@@ -960,7 +960,7 @@ dependencies = [
 
 [[package]]
 name = "exbyte-depot"
-version = "0.2.4"
+version = "0.3.0"
 dependencies = [
  "encoding_rs",
  "serde",