fix(tui): collapse multiline tool summaries so action rows don't stripe

file_read on a directory/file returns newline-bearing summaries; clip kept the
newlines, so the action row rendered multi-line with a background-filled stripe
and the listing leaking underneath. Flatten the summary to one line first.

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

@@ -451,7 +451,10 @@ func countSuffix(added, removed int) string {
 
 // actionToolText joins a tool label with a short, clipped result summary.
 func actionToolText(label, summary string) string {
-	s := strings.TrimSpace(summary)
+	// Collapse to a single line first: tool summaries (dir listings, file heads)
+	// often carry newlines, and a multi-line action row paints a background stripe
+	// per line with the raw content leaking underneath.
+	s := strings.Join(strings.Fields(summary), " ")
 	if s == "" {
 		return label
 	}