fix(tui): keep the steering note visible in the approval band

The steer note replaced the action row while editing and vanished once
you esc'd out — so you couldn't see the note or the approve/reject keys,
and it was unclear the note still applied (it did: decide() reads the
buffer). Now the note is a persistent line above the action row (editable
with a caret while typing, a dim reminder once set), and the action row
stays visible. Editing hints clarify enter=approve+send, esc=keep note.

apps/tui-go/internal/app/demo.go

@@ -84,6 +84,22 @@ func PreviewFrame(kind string, w, h int) string {
 			}
 		}
 
+	case "approval-steer":
+		m.connected = true
+		m.currentModel = "llama-cpp:default"
+		m.sessions = sampleSessions()
+		m.selectedID = "04a546aa"
+		m.sessionEntered = true
+		m.steerBuffer = "also print the current distro and kernel version"
+		if s := m.session("04a546aa"); s != nil {
+			s.CurrentStage = "write_script"
+			s.Pending = &Approval{
+				RequestID: "req-3", SessionID: "04a546aa", Tier: "T3", Risk: "MEDIUM",
+				ToolName: "file_write",
+				Preview:  "--- a/healthcheck.sh\n+++ b/healthcheck.sh\n@@ -0,0 +1,2 @@\n+#!/usr/bin/env bash\n+echo ok\n",
+			}
+		}
+
 	case "approval-shell":
 		m.connected = true
 		m.currentModel = "llama-cpp:default"