feat: TUI SFTP Browser Tab - Task 18

- SFTPBrowserTab with remote directory browsing
- Open via Ctrl+F from host list
- Navigate dirs, filter with /, refresh with r
- Dir/icon display with file sizes
- Sort dirs first, then by name

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/charmbracelet/bubbletea v1.3.10
 	github.com/charmbracelet/lipgloss v1.1.0
 	github.com/google/uuid v1.6.0
+	github.com/pkg/sftp v1.13.7
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
 	golang.org/x/crypto v0.53.0
@@ -27,6 +28,7 @@ require (
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/kr/fs v0.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-localereader v0.0.1 // indirect