Native-feel pass: PWA integration, system back, offline, haptics, undo

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

System integration
- Manifest: id, display_override, monochrome icon, Make my homework
  shortcut and a share target (text/URL via GET, files via POST).
  iOS startup images for the common iPhone sizes. Pinch-zoom is allowed
  again (double-tap zoom is disabled via touch-action instead).
- Share target: /share chooser with New deck / Make my homework; POSTed
  files wait in a 10-minute in-memory store, reach the wizard through
  sessionStorage and never touch disk.
- Web Share: Share rows for decks (JSON file where supported) and the
  homework result, with a clipboard fallback and a toast.
- Offline: a quiet pill appears and Freeze / mode cards are disabled
  with a clear reason; input is never lost (error cards keep Retry).
- State: wizard drafts (text, options, photos up to a size budget)
  survive reloads and OS kills and are cleared on success; re-tapping
  the active tab scrolls to the top; the deck page shows a skeleton
  instead of a spinner.

Navigation and gestures
- System Back closes the topmost layer first: a small history-entry
  stack (lib/use-back-close.ts) covers the drawer, Settings sheet,
  install sheet, deck actions panel and one wizard step; navigations
  are never rewound and stale entries are skipped.
- Destructive-but-reversible actions use Undo toasts: deleting a deck
  (no confirm) and removing a file in the wizard. Irreversible ones
  keep their confirm.

Input and feedback
- Every phone input got inputmode / enterkeyhint / autocomplete /
  autocapitalize / spellcheck; Enter on the last field advances the
  wizard; a clipboard-paste button appears where the API exists.
- Haptics behind a Settings toggle (on by default): tab switches,
  toggles, correct/wrong, completion; Vibration API + the iOS hidden
  switch tick, throttled and silent everywhere else.
- Wake lock during the study feed and homework guide, released on
  leave and re-acquired when the tab returns.

Verified: new native suite 35/35 (manifest/head/viewport, offline,
share target GET + POST, back-gesture layers, undo, share fallback,
tab re-tap, haptics persistence, draft restore), regression 74/74,
mobile 52/52, wizard 80/80, declutter 116/116, animation 8/8,
i18n 25/25. Lint + build clean. SW freezmo-v23.

Needs a real device (documented in the README): iOS haptic tick,
system share sheet entry, wake-lock grant, iPhone startup images,
iOS edge-swipe back, install prompts. Pull-to-refresh and the app
badge were skipped on purpose.

components/TabBar.tsx

@@ -5,6 +5,7 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 
 import { GearIcon, HomeIcon, PlusIcon } from "@/components/icons";
+import { haptic } from "@/lib/haptics";
 import { useI18n } from "@/lib/i18n";
 import { springSnappy } from "@/lib/motion";
 import { openSettings } from "@/lib/ui-events";
@@ -67,6 +68,14 @@ export function TabBar() {
         href="/"
         aria-current={libraryActive ? "page" : undefined}
         className={cn(item, libraryActive ? active : idle)}
+        onClick={(event) => {
+          haptic("tap");
+          // Re-tapping the active tab scrolls back to the top.
+          if (libraryActive) {
+            event.preventDefault();
+            window.scrollTo({ top: 0, behavior: reduceMotion ? "auto" : "smooth" });
+          }
+        }}
       >
         {pill(libraryActive)}
         {icon(<HomeIcon className="size-6" />, libraryActive, "library")}
@@ -76,6 +85,13 @@ export function TabBar() {
         href="/create"
         aria-current={createActive ? "page" : undefined}
         className={cn(item, createActive ? active : idle)}
+        onClick={(event) => {
+          haptic("tap");
+          if (createActive) {
+            event.preventDefault();
+            window.scrollTo({ top: 0, behavior: reduceMotion ? "auto" : "smooth" });
+          }
+        }}
       >
         {pill(createActive)}
         {icon(
@@ -87,7 +103,14 @@ export function TabBar() {
         )}
         {label(t("common.newDeck"), createActive)}
       </Link>
-      <button type="button" onClick={openSettings} className={cn(item, idle)}>
+      <button
+        type="button"
+        onClick={() => {
+          haptic("tap");
+          openSettings();
+        }}
+        className={cn(item, idle)}
+      >
         {icon(<GearIcon className="size-6" />, false, "settings")}
         {label(t("common.settings"), false)}
       </button>