Fix ordering giveaways, the stuck false label, add Regenerate deck

Ordering cards
- Generation prompt now forbids dates, years, times, step numbers and
  ordinals in ordering items (spec + hard rules), and the server-side
  validation drops any ordering card whose items still contain them
  instead of shipping a giveaway.

True/False
- The 'false ✕' swipe label was permanently visible on the card: its
  opacity curve was inverted, so the clamp at rest was 1. Flipped the
  range (and tightened both ranges for the elastic drag) — each label now
  only fades in while swiping in that direction.

Regenerate deck
- Results screen gains a Regenerate deck button: rebuilds the activities
  from the deck's stored source notes, replaces the deck in storage
  (attempts/best score reset) and starts the fresh run from slide 1.
- StudyFeed tracks the current deck so the header, export and messages use
  the regenerated title/activities.
- Fixed a spurious 0% attempt recorded when a regenerated deck swapped in:
  scroll anchoring held the old results position, so the feed briefly
  reported 5/5 with zero answers. The scroll now resets before the new
  slides render, overflow-anchor is disabled on the feed, and a run with
  no answers is never recorded.

Tests: new deck-fixes suite 15/15 (TF overlay at rest/drag, regenerate
with loading state + storage reset, ordering guard drop/keep); retry
14/14, deck chrome 15/15, pwa 16/16, final-ux 12/12, security 8/8,
contrast 20/20.

components/ResultsScreen.tsx

@@ -6,7 +6,7 @@ import { motion } from "framer-motion";
 import type { Activity, Deck } from "@/lib/schemas";
 import { downloadDeck } from "@/lib/storage";
 import { cn } from "@/lib/utils";
-import { BoltIcon, DownloadIcon, FlameIcon, HomeIcon, RefreshIcon, SnowflakeIcon } from "@/components/icons";
+import { BoltIcon, DownloadIcon, FlameIcon, HomeIcon, RefreshIcon, SnowflakeIcon, SparklesIcon } from "@/components/icons";
 import { Button, Chip } from "@/components/ui";
 
 import type { AttemptResult } from "./StudyFeed";
@@ -60,6 +60,9 @@ export function ResultsScreen({
   retryMode,
   onRetryMissed,
   onRestart,
+  onRegenerate,
+  regenerating,
+  regenerateError,
 }: {
   deck: Deck;
   xp: number;
@@ -71,6 +74,9 @@ export function ResultsScreen({
   retryMode: boolean;
   onRetryMissed: () => void;
   onRestart: () => void;
+  onRegenerate: () => void;
+  regenerating: boolean;
+  regenerateError: string | null;
 }) {
   const percent = total > 0 ? Math.round((correct / total) * 100) : 0;
   const perfect = missed.length === 0 && total > 0;
@@ -151,6 +157,21 @@ export function ResultsScreen({
             <RefreshIcon className="size-5" /> Study the whole deck again
           </Button>
         ) : null}
+        <Button
+          size="lg"
+          variant="secondary"
+          onClick={onRegenerate}
+          loading={regenerating}
+          disabled={regenerating}
+        >
+          <SparklesIcon className="size-5" />
+          {regenerating ? "Regenerating…" : "Regenerate deck"}
+        </Button>
+        {regenerateError ? (
+          <p className="text-center text-xs text-rose-600 dark:text-rose-300" role="alert">
+            {regenerateError}
+          </p>
+        ) : null}
         <div className="grid grid-cols-2 gap-2">
           <Button variant="ghost" onClick={() => downloadDeck(deck)}>
             <DownloadIcon className="size-4" /> Export JSON