Fix empty inline edit textarea expanding to full height

When the textarea content was empty, trimEndOfBufferLines stripped all
lines (including the cursor line) since they all appear as whitespace
after ANSI stripping. The fallback returned the full untrimmed view,
causing the edit box to fill the entire panel.

Fix by stopping the trim loop at 1 instead of 0, so the cursor line is
always preserved.

Assisted-By: cagent

Author: dgageot

pkg/tui/components/messages/messages.go

@@ -983,15 +983,13 @@ func trimEndOfBufferLines(view string) string {
 
 	// Trim trailing lines that are visually empty (whitespace-only after ANSI strip).
 	// Content lines always contain visible text or cursor escape sequences.
+	// Always keep at least one line so that an empty textarea still renders
+	// the cursor line instead of returning the full padded view.
 	last := len(lines)
-	for last > 0 && strings.TrimSpace(ansi.Strip(lines[last-1])) == "" {
+	for last > 1 && strings.TrimSpace(ansi.Strip(lines[last-1])) == "" {
 		last--
 	}
 
-	if last == 0 {
-		return view
-	}
-
 	return strings.Join(lines[:last], "\n")
 }