fix: complete vault layout transition — fs_path everywhere, no more spaces/

- notes.Create(): .md files stored in parent node's fs_path folder
- files.CopyIntoVault/CreateEmptyFile/Duplicate: use parent fs_path
- files.AddPathCopy/AddPathLink: use parent fs_path, set folder fs_path
- files.DeleteNodeAndChildren: move physical folder to .verstak/trash
- UpdateFsPathRecursive: use SafeDisplayNameToPathSegment(child.Title)
- sync_apply.go note ops: use fs_path instead of spaces/
- internal/gui/server.go file upload: use n.FsPath instead of nodeSlug
- VaultCheck diagnostic: walk nodes/files, verify paths on disk
- Tests: create/rename/move/delete/name-conflict/vault-check all pass

scripts/check-i18n.sh

@@ -25,6 +25,7 @@ ALLOWED_GO_CYRILLIC=(
   "cmd/verstak-gui/main.go"
   "internal/core/templates/safename.go"
   "internal/core/templates/safename_test.go"
+  "cmd/verstak-gui/vault_layout_test.go"
 )
 
 echo "=== Checking for hardcoded Cyrillic in source code ==="