Wrap toast bodies, slim the dismiss hint, and stop flicker

Toasts now render three content rows with word-wrapped bodies. The
in-toast "Ctrl-N · N more" hint is replaced by a short
"Ctrl-N · dismiss" entry on the status strip that only appears
while a notification is live.

The box stops flickering while the focused child repaints its TUI:
the overlay is stitched onto the per-chunk PTY write under outMu
and bracketed by DECSET 2026 so supporting terminals buffer the
child's redraw and the box paint into a single frame.

internal/app/app.go

@@ -969,14 +969,19 @@ func (st *uiState) OnPTYOut(childID string, chunk []byte) {
 			st.metrics.recordRender(time.Since(rstart))
 		}
 	}
-	// One write covers the autowrap-disable prelude, the chunk, and the
-	// autowrap-restore postlude — three syscalls collapsed into one
-	// under outMu. The three sequences were already emitted atomically
-	// under the lock; coalescing just halves the syscall count.
-	wrapped := make([]byte, 0, len(out)+10)
+	// One write covers the autowrap-disable prelude, the chunk, the
+	// autowrap-restore postlude, and (when a toast is up) the toast
+	// overlay — four syscalls collapsed into one under outMu. The
+	// sequences were already emitted atomically under the lock;
+	// coalescing just halves the syscall count and makes claude's
+	// continuous redraws + our toast layer land in the same frame so
+	// the box doesn't flicker as the child paints over its cells.
+	overlay := st.toastOverlayBytes()
+	wrapped := make([]byte, 0, len(out)+len(overlay)+10)
 	wrapped = append(wrapped, "\x1b[?7l"...)
 	wrapped = append(wrapped, out...)
 	wrapped = append(wrapped, "\x1b[?7h"...)
+	wrapped = append(wrapped, overlay...)
 	var wstart time.Time
 	if st.metrics != nil {
 		wstart = time.Now()
@@ -1219,6 +1224,12 @@ func (st *uiState) drawStatusLine() {
 			hints = append(hints, "Ctrl-R · restart")
 		}
 	}
+	// Surface the toast-dismiss chord only while a notification is on
+	// screen — the hint is noise otherwise, and Ctrl-N falls through
+	// to the focused PTY when the stack is empty.
+	if st.toasts.length() > 0 {
+		hints = append(hints, "Ctrl-N · dismiss")
+	}
 	right := strings.Join(hints, "  ·  ")
 	for len(hints) > 1 && int(cols)-len(left)-len(right) < 1 {
 		hints = hints[1:]