fix: form tab input not responding to typing

Bug: t.inputs[t.focus].Update(msg) discarded the returned textinput.Model,
so typed characters were never stored in the input state.

Fix: capture both updated model and cmd from textinput.Update():
  t.inputs[t.focus], cmd = t.inputs[t.focus].Update(msg)
  return t, cmd

Same fix applied to all 3 forms (host, key, snippet).
Also moved ctrl+s out of default to its own case for clarity.

pkg/tui/host_form_tab.go

@@ -154,11 +154,13 @@ func (t *HostFormTab) Update(msg tea.Msg) (Tab, tea.Cmd) {
 		case "shift+tab", "up":
 			t.prevField()
 
+		case "ctrl+s":
+			return t.submit()
+
 		default:
-			if msg.String() == "ctrl+s" {
-				return t.submit()
-			}
-			t.inputs[t.focus].Update(msg)
+			var cmd tea.Cmd
+			t.inputs[t.focus], cmd = t.inputs[t.focus].Update(msg)
+			return t, cmd
 		}
 	}