test(interactive): replace blind y-loops with accept_until helper

Add an accept_until helper that only sends "y" when a new [Y/n] prompt
appears in the tmux pane, replacing the fixed-count blind send loops that
could race ahead of prompts or send stray input. Resilient to changes in
the number of apply-phase prompts.

Relates to #51

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/interactive/test-signing-generate.sh

@@ -34,19 +34,8 @@ main() {
     wait_for "Proceed with hardening"
     send "y" Enter
 
-    # Accept settings until signing wizard (v0.2.0 adds more prompts)
-    local pane_content
-    for _ in $(seq 1 50); do
-        sleep 0.3
-        pane_content="$(tmux capture-pane -t "$TMUX_SESSION" -p 2>/dev/null || true)"
-        if printf '%s' "$pane_content" | grep -qF "Signing key options"; then
-            break
-        fi
-        if printf '%s' "$pane_content" | grep -qF "Hardening complete"; then
-            break
-        fi
-        send "y" Enter
-    done
+    # Accept all [Y/n] prompts until signing wizard
+    accept_until "Signing key options"
 
     # Signing wizard — option 1: generate ed25519
     wait_for "Signing key options" 20