chore: scaffold, CI, and the export bundle verbatim

The export bundle is the input to this port, not a sketch: the curriculum,
the tutor prompt and the five logic modules are finished and tested. They
land here byte-identical and stay that way.

  diff -r export/data data && diff -r export/lib lib
  diff -r export/prompt prompt && diff export/validate.mjs validate.mjs

data/, lib/, prompt/ and validate.mjs sit at the repo root so validate.mjs
runs verbatim with no path edits. All four are excluded from lint and
formatting — they are not ours to restyle. Types for lib/ live alongside in
types/ rather than as sibling .d.ts files, so the verbatim check stays a
plain directory diff.

CI runs the curriculum gate first, before anything else can pass:

  node validate.mjs   PASS — 0 blocking, 0 advisory

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

lib/srs.js

@@ -0,0 +1,46 @@
+/* SM-2 lite. Four grades, day-granularity intervals. */
+export const AGAIN = 0, HARD = 1, GOOD = 2, EASY = 3;
+export const NEW = 0, LEARNING = 1, REVIEW = 2;
+export const SECURE_INTERVAL = 21;          // days at which a card counts as known
+
+export const newCard = () => ({ state: NEW, interval: 0, ease: 2.5, due: 0, reps: 0, lapses: 0 });
+
+export function grade(card, g, today) {
+  const c = { ...card };
+  if (c.state === NEW || c.state === LEARNING) {
+    if (g <= HARD)      { c.state = LEARNING; c.interval = 0; c.due = today; }
+    else if (g === GOOD){ c.state = REVIEW;   c.interval = 1; c.due = today + 1; }
+    else                { c.state = REVIEW;   c.interval = 4; c.due = today + 4; }
+  } else {
+    if (g === AGAIN)     { c.ease = Math.max(1.3, c.ease - 0.2);  c.lapses++; c.state = LEARNING; c.interval = 0; c.due = today; }
+    else if (g === HARD) { c.ease = Math.max(1.3, c.ease - 0.15); c.interval = Math.max(1, Math.round(c.interval * 1.2)); c.due = today + c.interval; }
+    else if (g === GOOD) { c.interval = Math.max(1, Math.round(c.interval * c.ease)); c.due = today + c.interval; }
+    else                 { c.ease = Math.min(3, c.ease + 0.15); c.interval = Math.max(2, Math.round(c.interval * c.ease * 1.3)); c.due = today + c.interval; }
+    c.interval = Math.min(c.interval, 365);
+    c.due = Math.min(c.due, today + 365);
+  }
+  c.reps++;
+  return c;
+}
+
+export const markKnown = today => ({ state: REVIEW, interval: SECURE_INTERVAL, ease: 2.5, due: today + SECURE_INTERVAL, reps: 0, lapses: 0 });
+
+export function statusOf(card) {
+  if (!card || card.state === NEW) return "new";
+  if (card.state === LEARNING) return "learning";
+  return card.interval >= SECURE_INTERVAL ? "secure" : "review";
+}
+
+/** Label for the interval a grade would produce — shown on the buttons. */
+export function preview(card, g, today) {
+  const c = grade(card || newCard(), g, today);
+  if (c.interval === 0)  return "again now";
+  if (c.interval === 1)  return "1 day";
+  if (c.interval < 30)   return `${c.interval} days`;
+  const mo = Math.round(c.interval / 30);
+  return `${mo} month${mo === 1 ? "" : "s"}`;
+}
+
+/** Local day number, DST-safe. */
+export const dayNumber = (d = new Date()) =>
+  Math.floor(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()) / 864e5);