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/globals.css

@@ -492,6 +492,28 @@ body {
   background-image: linear-gradient(135deg, #38bdf8 0%, #60a5fa 100%);
   color: #06111f;
 }
+/* Link segments (library tabs): same control, but links navigate. */
+.segmented > a {
+  flex: 1;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: 0.375rem;
+  border-radius: 0.75rem;
+  padding: 0.42rem 0.5rem;
+  font-size: 0.875rem;
+  font-weight: 600;
+  color: var(--color-frost-700);
+  transition: background-color 0.18s ease, color 0.18s ease, box-shadow 0.18s ease;
+}
+.dark .segmented > a {
+  color: var(--color-frost-300);
+}
+.segmented > a[aria-current="page"] {
+  background-image: linear-gradient(135deg, #38bdf8 0%, #60a5fa 100%);
+  color: #06111f;
+  box-shadow: 0 6px 16px -8px rgb(56 189 248 / 0.7);
+}
 
 /* Ice gradient for progress bars and selected states. */
 .grad-ice {
@@ -705,7 +727,8 @@ body {
 @media (max-width: 639px) {
   .touch-target { min-height: 44px; min-width: 44px; }
   .nav-row { min-height: 44px; }
-  .segmented > button { min-height: 44px; }
+  .segmented > button,
+  .segmented > a { min-height: 44px; }
   .folder-pill { min-height: 44px; }
 }