Navigation restructure: five-tab bottom bar, no phone drawer

Drawer removed (phones only; desktop rail untouched)
- MobileSidebar, sidebarOpen/useSidebarOpen, MenuIcon and the drawer's
  back-gesture layer are gone; the shared nav content now serves only
  the desktop rail (dead mobile branches deleted). No drawer-specific
  CSS existed; the three drawer strings (header.openMenu,
  sidebar.closeMenu, common.menu) and library.importAria are removed.
- The header drops the hamburger: logo + name on the left, the single
  theme chip on the right.

Five-tab bottom bar
- Library / Progress / New deck (prominent centre +) / Exam / Settings,
  in that order; Progress and Exam reuse the existing /stats and /exam
  screens, Settings keeps opening the dialog. Sliding pill, icon bounce,
  press feedback, re-tap-to-top and safe-area padding kept; every item
  is >=44px (72px wide at 360px).
- New short tab.* keys (EN + CS) so all five labels stay on one line at
  360px — 'Zkouškový režim' became 'Zkouška'. No ellipsis anywhere.
- The bar is mounted once in AppHeader so library, progress, exam and
  share get it; the wizards keep their own bottom action bar and the
  tab bar steps aside there, exactly as before.

Re-homed drawer destinations
- Smart Review card loses the Exam link (it is a tab now); Review due
  and Mistakes stay.
- New deck screen (and /homework) get a Study deck / Make my homework
  segmented switch; the library's homework empty-state button stays.
- The phone import icon becomes a ... button opening a sheet with
  Import JSON and New folder (back-gesture and Escape close it); folder
  chips still appear only once at least one folder exists, and folder
  creation stays in the New deck options step.

Verified: mobile suite 134 checks (no hamburger/drawer, tab order and
44px targets, label matrix at 360/390 x EN/CS x dark/light x reduced
motion, per-tab routing, deep links, Back from every tab, the ... sheet
with folder creation) plus regression 74/74, wizard 83/83, declutter
116/116, animation 8/8, native 35/35, i18n 25/25, phase1 38/38, phase2
43/43, phase3 20/20, freeze-loading 6/6. Key parity 740/740. Lint +
build clean. SW freezmo-v28.

components/AppHeader.tsx

@@ -3,18 +3,17 @@
 import Link from "next/link";
 import { useEffect, useState } from "react";
 
-import { MenuIcon } from "@/components/icons";
 import { SettingsDialog } from "@/components/SettingsDialog";
+import { TabBar } from "@/components/TabBar";
 import { ThemeToggle } from "@/components/ThemeToggle";
 import { useI18n } from "@/lib/i18n";
-import { sidebarOpen } from "@/lib/nav";
 import { OPEN_SETTINGS_EVENT } from "@/lib/ui-events";
 import { cn } from "@/lib/utils";
 
 /**
- * Minimal, sticky frosted top bar: brand on the left, quiet actions on the
- * right. The phone layout keeps the brand compact and relies on the tab bar
- * for navigation.
+ * Minimal, sticky frosted top bar: brand on the left, theme chip on the
+ * right. Phones navigate with the bottom tab bar (also mounted here, so every
+ * screen that has a header gets it); the desktop rail carries navigation.
  */
 export function AppHeader({ className, compact = false }: { className?: string; compact?: boolean }) {
   const { t } = useI18n();
@@ -48,41 +47,34 @@ export function AppHeader({ className, compact = false }: { className?: string;
         )}
       >
         <div className="mx-auto flex h-14 max-w-6xl items-center justify-between gap-3">
-          <button
-            type="button"
-            onClick={() => sidebarOpen.toggle()}
-            aria-label={t("header.openMenu")}
-            className="mr-1 grid size-9 shrink-0 touch-target place-items-center rounded-full text-[var(--text-muted)] transition hover:bg-[var(--hover)] hover:text-[var(--text)]"
+          <Link
+            href="/"
+            className="group flex min-w-0 items-center gap-2.5 rounded-xl px-1 py-1"
+            aria-label={t("header.home")}
           >
-            <MenuIcon className="size-5" />
-          </button>
-          <Link href="/" className="group flex items-center gap-2.5 rounded-xl px-1 py-1" aria-label={t("header.home")}>
-          {/* eslint-disable-next-line @next/next/no-img-element -- static app icon, no optimisation needed */}
-          <img
-            src="/icons/icon-192.png"
-            alt=""
-            aria-hidden
-            className="size-8 rounded-[0.6rem] transition-transform group-hover:scale-[1.04]"
-          />
-            <span className="flex items-baseline gap-2">
-              <span className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">
-                Freezmo
-              </span>
+            {/* eslint-disable-next-line @next/next/no-img-element -- static app icon, no optimisation needed */}
+            <img
+              src="/icons/icon-192.png"
+              alt=""
+              aria-hidden
+              className="size-8 shrink-0 rounded-[0.6rem] transition-transform group-hover:scale-[1.04]"
+            />
+            <span className="flex min-w-0 items-baseline gap-2">
+              <span className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">Freezmo</span>
               {!compact ? (
-                <span className="hidden text-[13px] text-[var(--text-subtle)] sm:inline">
+                <span className="hidden truncate text-[13px] text-[var(--text-subtle)] sm:inline">
                   {t("header.tagline")}
                 </span>
               ) : null}
             </span>
           </Link>
 
-          <div className="flex items-center gap-1">
-            {/* Settings lives in the tab bar and the drawer; the old header
-                gear was the same control a third time. */}
+          <div className="flex shrink-0 items-center gap-1">
             <ThemeToggle />
           </div>
         </div>
       </header>
+      <TabBar />
       <SettingsDialog
         open={settingsOpen}
         onClose={() => setSettingsOpen(false)}