Phase 3: Check my work, follow-ups and turn-into-deck

Check my work (third homework mode)
- One model call with its own system prompt marks the student's own
  attempt: verdict, what's right, each issue with why + fix, and the
  corrected version that keeps everything the student got right.
  Unasked-for extras are never errors. The attempt is typed/pasted
  (photos of handwriting are documented as unsupported) and stored in
  the record so Redo re-checks the same work.
- Server: mode "check" + solution on POST /api/homework (zod, 400
  server.needSolution without one) and the same NDJSON stream; new
  checkHomework() pipeline with repair-once validation.

Follow-ups
- New POST /api/homework/refine (plain JSON, RATE_LIMIT_REFINE, zod,
  auth before body): shorter / more detail / explain, plain text back,
  language preserved.
- Shorter + More detail + Original rewrite the finished answer and the
  corrected version in place (FollowUpBar); every guide step has
  Explain step N differently; failed calls say so without losing text.

Turn into a study deck
- Any result hands its content (answer, corrected version or assembled
  guide) to New deck through a one-shot sessionStorage seed with the
  options step pre-filled.

UI
- Phone step 2 gains the third card: tapping it reveals the solution
  field + submit; desktop has three cards and the solution field shows
  with the mode. Homework history labels and share/card previews cover
  the new mode.

Verified: new phase-3 suite 20/20 against a stub Ollama (check payload,
missing-solution 400, refine validation, phone + desktop check flows,
shorter follow-up with restore, guide explain, deck hand-off) plus
regression 74/74, mobile 52/52, declutter 116/116, wizard 80/80,
animation 8/8, native 35/35, phase1 38/38, phase2 43/43, i18n 25/25.
Key parity 734/734. Lint + build clean. SW freezmo-v27.

components/UploadScreen.tsx

@@ -32,6 +32,7 @@ import { useI18n } from "@/lib/i18n";
 import { stepVariants } from "@/lib/motion";
 import { UNORGANIZED_ID, type Difficulty } from "@/lib/schemas";
 import { takePendingShare } from "@/lib/share-pending";
+import { takeDeckSeed } from "@/lib/deck-seed";
 import { upsertDeck } from "@/lib/storage";
 import { showToast } from "@/lib/toast";
 import { openSettings } from "@/lib/ui-events";
@@ -308,6 +309,15 @@ export function UploadScreen() {
     if (pending.files.length > 0) void addFiles(pending.files);
   }, [addFiles]);
 
+  /* Homework → "Turn into a study deck": content + options pre-filled. */
+  useEffect(() => {
+    const seed = takeDeckSeed();
+    if (!seed) return;
+    setText(seed.text);
+    if (seed.difficulty) setDifficulty(seed.difficulty);
+    if (seed.count) setCount(seed.count);
+  }, []);
+
   /* Persist the draft while the user works (debounced, best-effort). */
   useEffect(() => {
     if (phase === "loading") return;