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

pkg/tui/host_list_tab.go

@@ -75,6 +75,14 @@ func (t *HostListTab) Update(msg tea.Msg) (Tab, tea.Cmd) {
 				}
 			}
 
+		case "ctrl+f":
+			if len(t.hosts) > 0 {
+				host := t.hosts[t.selectedIndex]
+				return t, func() tea.Msg {
+					return openSFTPMsg{host: host}
+				}
+			}
+
 		case "q", "ctrl+c":
 			return t, func() tea.Msg {
 				return quitMsg{}