feat(shell): scrollable status tabs, per-page tab titles, skip-to-content, Czech MUI locale

- Shared Tabs: variant=scrollable + auto scroll buttons — the 5 status-filter
  tabs no longer clip unreachable at ~360px (desktop rendering unchanged).
- TitleSync: browser tab shows the active page ('Faktury · BOHA'; ambiguous
  labels qualified with their section, e.g. 'Záznam – Docházka · BOHA');
  index.html fallback now 'BOHA Admin'.
- Skip-to-content link (visually hidden, visible on focus) + id/tabIndex on
  <main> — keyboard users skip the 248px sidebar.
- MUI csCZ locale merged into the theme (kills built-in English strings like
  'No options'); Czech noOptionsText on Customer/Supplier pickers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/ui/AppShell.tsx

@@ -11,6 +11,7 @@ import { setLogoutAlert } from "../utils/api";
 import SidebarNav from "./SidebarNav";
 import LoadingState from "./LoadingState";
 import ShortcutsHelp from "../components/ShortcutsHelp";
+import TitleSync from "../components/TitleSync";
 
 const DRAWER_WIDTH = 248;
 
@@ -98,6 +99,7 @@ export default function AppShell() {
 
   return (
     <ScopedCssBaseline>
+      <TitleSync />
       <motion.div
         initial={{ opacity: 0, scale: 0.98 }}
         animate={
@@ -110,6 +112,38 @@ export default function AppShell() {
           ease: [0.4, 0, 0.2, 1],
         }}
       >
+        {/* Skip link: first focusable element; visually hidden (clipped)
+            until keyboard focus reveals it above the drawer. */}
+        <Box
+          component="a"
+          href="#main-content"
+          sx={(theme) => ({
+            position: "absolute",
+            top: 8,
+            left: 8,
+            zIndex: theme.zIndex.drawer + 2,
+            width: "1px",
+            height: "1px",
+            overflow: "hidden",
+            clipPath: "inset(50%)",
+            whiteSpace: "nowrap",
+            px: 2,
+            py: 1,
+            borderRadius: 1,
+            bgcolor: theme.vars!.palette.primary.main,
+            color: theme.vars!.palette.primary.contrastText,
+            textDecoration: "none",
+            fontWeight: 600,
+            "&:focus": {
+              width: "auto",
+              height: "auto",
+              overflow: "visible",
+              clipPath: "none",
+            },
+          })}
+        >
+          Přeskočit na obsah
+        </Box>
         <Box
           sx={{
             display: "flex",
@@ -209,10 +243,15 @@ export default function AppShell() {
             </Box>
             <Box
               component="main"
+              id="main-content"
+              tabIndex={-1}
               sx={{
                 flex: 1,
                 px: immersiveOnMobile ? { xs: 0, md: 3 } : { xs: 2, md: 3 },
                 pb: immersiveOnMobile ? { xs: 0, md: 4 } : 4,
+                // Skip-link target: focus lands here programmatically — the
+                // region-wide focus ring would be noise, not a signal.
+                "&:focus": { outline: "none" },
                 ...(immersiveOnMobile && {
                   minHeight: 0,
                   overflow: { xs: "hidden", md: "visible" },