feat: Task 16 — SSH Session Tab (multi-session)

- pkg/tui/session.go — SessionTab with live SSH terminal in a tab
- pkg/tui/messages.go — quitMsg, openSessionMsg, sessionOutputMsg
- pkg/tui/tabs.go — Tab.Close() interface, Add() returns tea.Cmd
- pkg/tui/host_list_tab.go — Enter opens session tab, q quits
- pkg/tui/tui.go — handle openSessionMsg/quitMsg, SetDataDir
- cmd/hostkeeper/tui.go — pass dataDir to model

pkg/tui/tabs.go

@@ -12,6 +12,8 @@ type Tab interface {
 	Update(tea.Msg) (Tab, tea.Cmd)
 	View() string
 	Name() string
+	// Close is called when the tab is removed; implement for cleanup (e.g. disconnect SSH)
+	Close()
 }
 
 // TabManager manages multiple tabs
@@ -38,10 +40,11 @@ func (tm *TabManager) Active() Tab {
 	return tm.tabs[tm.active]
 }
 
-// Add adds a new tab and switches to it
-func (tm *TabManager) Add(tab Tab) {
+// Add adds a new tab, switches to it, and returns its init command
+func (tm *TabManager) Add(tab Tab) tea.Cmd {
 	tm.tabs = append(tm.tabs, tab)
 	tm.active = len(tm.tabs) - 1
+	return tab.Init()
 }
 
 // Close removes the tab at index and returns the active tab
@@ -50,6 +53,9 @@ func (tm *TabManager) Close(index int) Tab {
 		return nil
 	}
 
+	// Call Close for cleanup (e.g. disconnect SSH)
+	tm.tabs[index].Close()
+
 	tm.tabs = append(tm.tabs[:index], tm.tabs[index+1:]...)
 
 	if len(tm.tabs) == 0 {