fix(story-mode): no celebration when the turn is not a clean finish

From review round 8: "Mission complete!" with confetti and cheering
helpers sat over balloons saying the page will not work as opened, a
helper's tests have not run, or a problem is left. The final panel is now
calm (no confetti, a neutral robot) whenever work was still out at the
turn's end, nothing worked, or Claude's last words name an open problem
(`page.openNote`: a key point about something wrong, not done, not
checked or not fixed); the last of these reads "Done, with a catch".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/fixtures/story-corpus/python-cli-fix-loop.expected.json

@@ -12,6 +12,7 @@
     "helpers": 0,
     "helpersRunning": 0,
     "finishedLater": 0,
+    "openNote": false,
     "panels": [
       {
         "kind": "mission",