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/SeriesSettings.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import {
   Button,
   Column,
@@ -20,7 +20,7 @@ import { confirm } from "@tauri-apps/plugin-dialog";
 import { api } from "../lib/api";
 import type { InvoiceSeries } from "../lib/types";
 
-export default function SeriesSettings() {
+export default function SeriesSettings({ active: visible }: { active: boolean }) {
   const [active, setActive] = useState<InvoiceSeries | null>(null);
   const [all, setAll] = useState<InvoiceSeries[]>([]);
   const [loading, setLoading] = useState(true);
@@ -31,14 +31,18 @@ export default function SeriesSettings() {
   const [error, setError] = useState<string | null>(null);
   const [notice, setNotice] = useState<string | null>(null);
 
+  const seeded = useRef(false);
+
   const load = async () => {
     try {
       const [current, list] = await Promise.all([api.getActiveSeries(), api.listSeries()]);
       setActive(current);
       setAll(list);
-      if (current) {
+      // Only seed the form once, so a refetch on re-entry does not overwrite what was typed.
+      if (current && !seeded.current) {
         setPrefix(current.prefix);
         setPadding(current.padding);
+        seeded.current = true;
       }
       setError(null);
     } catch (e) {
@@ -48,9 +52,10 @@ export default function SeriesSettings() {
     }
   };
 
+  // The view stays mounted, so refetch every time it is shown again.
   useEffect(() => {
-    void load();
-  }, []);
+    if (visible) void load();
+  }, [visible]);
 
   const startNew = async () => {
     const ok = await confirm(