feat: TUI Host Forms (add/edit) - Task 17

- HostFormTab with textinput fields for all host fields
- Add (Ctrl+N) and Edit (Ctrl+E) from host list
- Save to JSON storage, auto-reload on save
- Esc to cancel, navigable form with keyboard

pkg/tui/messages.go

@@ -1,14 +1,20 @@
 package tui
 
-import "git.tukangketik.id/swanadiva/hostkeeper/internal/models"
+import (
+	"context"
+
+	tea "github.com/charmbracelet/bubbletea"
+
+	"git.tukangketik.id/swanadiva/hostkeeper/internal/models"
+	"git.tukangketik.id/swanadiva/hostkeeper/pkg/storage"
+)
 
 // quitMsg signals the TUI to exit
 type quitMsg struct{}
 
 // openSessionMsg signals the TUI to open a new SSH session tab
 type openSessionMsg struct {
-	host    *models.Host
-	dataDir string
+	host *models.Host
 }
 
 // sessionOutputMsg carries SSH output to the TUI renderer
@@ -18,3 +24,43 @@ type sessionOutputMsg string
 type sessionDoneMsg struct {
 	err error
 }
+
+// openHostFormMsg signals the TUI to open a host form tab
+type openHostFormMsg struct {
+	editing *models.Host // nil for add mode
+}
+
+// closeFormMsg signals the TUI to close the active form tab
+type closeFormMsg struct{}
+
+// saveHostMsg is produced when the form needs to save a host
+type saveHostMsg struct {
+	host    *models.Host
+	dataDir string
+}
+
+// saveHostResultMsg is produced after a save attempt
+type saveHostResultMsg struct {
+	host *models.Host
+	err  error
+}
+
+// loadedHostsMsg is produced after reloading hosts from storage
+type loadedHostsMsg struct {
+	hosts []*models.Host
+}
+
+// saveHostCmd creates a command that saves a host to storage
+func saveHostCmd(host *models.Host, dataDir string) tea.Cmd {
+	return func() tea.Msg {
+		store, err := storage.NewJSONStorage(dataDir)
+		if err != nil {
+			return saveHostResultMsg{err: err}
+		}
+		ctx := context.Background()
+		if err := store.SaveHost(ctx, host); err != nil {
+			return saveHostResultMsg{err: err}
+		}
+		return saveHostResultMsg{host: host}
+	}
+}