tui: add userMessages helper to model type

cmd/sidekick-tui/main.go

@@ -80,6 +80,16 @@ func (m model) formatReasoning(reasoning string) string {
   return "> *Thinking:*\n>\n" + strings.Join(lines, "\n") + "\n"
 }
 
+func (m model) userMessages() []string {
+  var msgs []string
+  for _, msg := range m.history {
+    if msg.Role == sidekick.MessageRoleUser {
+      msgs = append(msgs, msg.Content)
+    }
+  }
+  return msgs
+}
+
 type agentResponseMsg struct {
   response string
   err      error