Add useSftp composable with mock directory listings, path navigation,
and refresh. FileTree component shows path bar, toolbar (upload,
download, new folder, refresh, delete icons), file entries with
icons, humanized sizes, and dates. TransferProgress component shows
expandable transfer list with progress bars. SidebarToggle now
uses v-model to emit tab changes. MainLayout switches between
ConnectionTree and FileTree based on sidebar tab, and includes
TransferProgress panel. File double-click emits openFile event
for the editor integration.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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