Animation pass: one shared motion language for phones

Mobile only (<=639px / coarse pointers); desktop keeps its behaviour.

Foundation
- lib/motion.ts owns the spring presets (snappy/gentle/sheet), durations,
  easings and variants (screens, tabs, wizard steps, list stagger).
- Native-feel CSS: press feedback scales every button, card, chip, tab,
  row and summary to 0.96 with a spring-like cubic-bezier on transform
  (scoped to phones/coarse pointers), tap-highlight off, touch-action
  manipulation, chrome text non-selectable, reduced motion drops it.
- App shell fades in once on launch; the study feed fades in on phones.

Applied
- Tab bar: sliding active pill (shared layoutId) + icon bounce.
- Study Decks/Homework, language toggle, difficulty and size pickers:
  the same gliding highlight, gated so desktop keeps the old styling.
- Route content enters direction-aware (deeper = from the right, back =
  from the left, same-depth = crossfade) via RouteTransition on the
  library/create/homework content columns; library tab switches
  crossfade; wizard steps slide forward/backward (reduced motion safe).
- Library: cards fade up in a capped stagger on first load, glide with
  layout animations and shrink away on delete (AnimatePresence).
- Study feed: correct feedback pulses, wrong shakes, the progress bar
  settles with a spring curve, score and XP count up on the results.
- Settings sheet uses the sheet spring; the drawer now follows the
  finger and closes on release velocity, like the sheet.
- Generation progress: the stage message fades/slides between stages;
  the icon keeps its gentle wobble; the feed fades in on hand-off.

Skipped, on purpose: LazyMotion (the sliding highlights need layout
animations = domMax, same features the current import already has);
route exit animations (the App Router unmounts the outgoing page —
exits are handled by in-page AnimatePresence); replacing the study
feed's native scroll-snap with finger-follow drag (would fight the
platform scroller); finger-follow height animation for native <details>
expanders.

Verified: animation suite 8/8 (reduced motion + 4x-CPU-throttled trace:
no long tasks, CLS 0.0000), regression 74/74, mobile 52/52, declutter
116/116, i18n 25/25. Lint + build clean. SW freezmo-v21.

components/HomeworkCard.tsx

@@ -1,24 +1,43 @@
 "use client";
 
+import { motion } from "framer-motion";
 import Link from "next/link";
 import { useState } from "react";
 
 import { BoltIcon, ChevronDownIcon, PlayIcon, XIcon } from "@/components/icons";
 import { Button } from "@/components/ui";
 import { useI18n } from "@/lib/i18n";
+import { springGentle } from "@/lib/motion";
 import type { HomeworkRecord } from "@/lib/schemas";
+import { useIsPhone } from "@/lib/use-phone";
 import { cn, formatDate, truncate } from "@/lib/utils";
 
 /**
  * One saved homework result in the library's Homework tab: the finished
  * solution or the step-by-step guide, with open + delete.
  */
-export function HomeworkCard({ record, onDelete }: { record: HomeworkRecord; onDelete: (id: string) => void }) {
+export function HomeworkCard({
+  record,
+  onDelete,
+  index = 0,
+}: {
+  record: HomeworkRecord;
+  onDelete: (id: string) => void;
+  /** Position in the list — used for the capped first-load stagger. */
+  index?: number;
+}) {
   const { t, plural } = useI18n();
+  const isPhone = useIsPhone();
   const [confirmDelete, setConfirmDelete] = useState(false);
   const [expanded, setExpanded] = useState(false);
   const href = `/homework?open=${record.id}`;
 
+  const cardVariants = {
+    hidden: { opacity: 0, y: 12 },
+    show: { opacity: 1, y: 0, transition: { ...springGentle, delay: Math.min(index, 8) * 0.04 } },
+    exit: { opacity: 0, scale: 0.97, transition: { duration: 0.16 } },
+  };
+
   const preview =
     record.mode === "make"
       ? truncate(record.answer.replace(/\s+/g, " ").trim(), 150)
@@ -28,7 +47,14 @@ export function HomeworkCard({ record, onDelete }: { record: HomeworkRecord; onD
         );
 
   return (
-    <li className="card card-hover group relative flex flex-col p-4 sm:p-5">
+    <motion.li
+      layout={isPhone}
+      variants={isPhone ? cardVariants : undefined}
+      initial={isPhone ? "hidden" : false}
+      animate={isPhone ? "show" : undefined}
+      exit={isPhone ? "exit" : undefined}
+      className="card card-hover group relative flex flex-col p-4 sm:p-5"
+    >
       {/* Phones: the whole card opens the result too; the delete button sits above it. */}
       <Link href={href} aria-hidden="true" tabIndex={-1} className="absolute inset-0 hidden rounded-[1.5rem] max-sm:block lg:block" />
 
@@ -113,6 +139,6 @@ export function HomeworkCard({ record, onDelete }: { record: HomeworkRecord; onD
           </>
         )}
       </div>
-    </li>
+    </motion.li>
   );
 }