Separate Study Decks and Homework in the library; drop the /create mode switch

Library ("Your icebox")
- Two tabs, never mixed: Study Decks (the folder + card library) and Homework
  (saved solutions and step-by-step guides). The active tab lives in the URL
  (/?tab=homework), so the sections are linkable and survive a reload.
- Decks tab keeps Import, the folder bar, stats and its own empty state — now
  a single decks-only CTA.
- Homework tab lists saved results as cards (mode icon, date, step count,
  preview) with Open and delete-with-confirm; its empty state has its own CTA
  ("Homework Solver") that opens the solver directly. Opening a card
  deep-links to /homework?open=<id>, which the screen opens on arrival.
- .segmented now also styles link segments (same control as settings).

/create
- The redundant "Study Deck | Homework Solver" toggle is gone: /create is the
  deck uploader only, and the bottom bar's + goes straight to it. Homework has
  its own screen, reached from the library tab, the drawer and CTAs.

Copy
- New keys (en + cs): tabDecks, tabHomework, homeworkHeroTitle, plus homework
  empty-state/open/step-count strings. The homework hero is now "Solve your
  homework" / "Vyřeš svůj úkol" — no study-deck text in the homework flow.
- Removed the now-unused ModeSwitch component and homework.title key.

Service worker: freezmo-v10.

Verified: library-tabs suite 37/37 (tab switching, context empty states,
deep-link opening, deletion, no switch on /create, heroes, redirects, desktop
grid, 360px + 44px targets, axe contrast en+cs light+dark), mobile 49/49,
i18n 27/27, desktop regression 74/74. Lint + build clean.

app/homework/page.tsx

@@ -15,7 +15,7 @@ export default async function HomeworkPage({
 }: {
   searchParams: Promise<{ [key: string]: string | string[] | undefined }>;
 }) {
-  const { mode } = await searchParams;
+  const { mode, open } = await searchParams;
   // The mode switch and the library quick actions deep-link into a mode; a
   // link that points at the Study Deck side is handed back to /create.
   if (mode === "deck") redirect("/create?mode=deck");
@@ -29,7 +29,7 @@ export default async function HomeworkPage({
         <main className="flex min-h-dvh min-w-0 flex-1 flex-col">
           <AppHeader />
           <div className="mx-auto w-full max-w-3xl flex-1 px-4 pb-tabbar lg:px-10 lg:pb-16 lg:pt-10">
-            <HomeworkScreen />
+            <HomeworkScreen initialRecordId={typeof open === "string" ? open : undefined} />
           </div>
           <TabBar />
         </main>