Add invoice drafts, read-only issued state and keyboard shortcuts

Views stay mounted so switching tabs no longer loses a half-typed invoice.
The form autosaves a draft after 1 s, drafts can be resumed or deleted,
and after issuing the form is read-only with Export again, Duplicate and
New invoice actions. A failed export keeps the issued invoice and offers a
retry instead of issuing again. Adds Ctrl+N/S/Enter/L and a shortcut sheet;
F5 and Ctrl+R are blocked in production builds.

src/views/InvoiceHistory.tsx

@@ -20,7 +20,7 @@ import { formatAmount, formatDate } from "../lib/format";
 import { exportInvoicePdf } from "../lib/pdf";
 import type { InvoiceSummary, Settings } from "../lib/types";
 
-export default function InvoiceHistory({ settings }: { settings: Settings }) {
+export default function InvoiceHistory({ settings, active }: { settings: Settings; active: boolean }) {
   const [rows, setRows] = useState<InvoiceSummary[]>([]);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
@@ -39,9 +39,10 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
     }
   };
 
+  // The view stays mounted, so refetch every time it is shown again.
   useEffect(() => {
-    void load();
-  }, []);
+    if (active) void load();
+  }, [active]);
 
   const onExport = async (id: number) => {
     setBusyId(id);