fix(tui): pin footer to bottom, style hint bar, auto-clear status

Content area now enforces full height so the context help bar stays
pinned to the terminal bottom. Hint keys rendered with bold highlight
color for scannability. Status messages (created, deleted, etc.)
auto-clear after 2 seconds, reverting to the entity count.

internal/tui/styles.go

@@ -122,4 +122,11 @@ var (
 
 	separatorStyle = lipgloss.NewStyle().
 			Foreground(dim)
+
+	hintKeyStyle = lipgloss.NewStyle().
+			Foreground(highlight).
+			Bold(true)
+
+	hintDescStyle = lipgloss.NewStyle().
+			Foreground(dim)
 )