Add the ERPNext settings UI, History and detail controls, and voiced.invoice.v1 export (Phase F3)

- Settings gets an Integrations tab: connection fields with a write-only API secret, a CA PEM option, Test connection with versions and warnings, live mapping lists loaded after a test, naming mode, toggles and its own Save.
- Pushing for a GST-registered vendor is refused until a connection test result is stored. The UI shows the reason and disables Send.
- History shows an ERPNext status column from one bulk call, a row Send and Open in ERPNext, and a bulk Send selected with a draft-or-submit confirm step and per-row results that never abort the batch. The detail view gets an ERPNext panel and per-payment send. All of it is hidden or disabled when the integration is not configured.
- Optional auto-push after issue runs in the background and never blocks or fails the issue.
- Generic export: a deterministic voiced.invoice.v1 JSON (and CSV line items) for selected invoices, documented in docs/voiced-invoice-v1.md with a golden test. Money is integer paise plus a decimal string.

The new screens have not been run in a webview yet. The ERPNext Payment Entry deduction fields still need a live check.

src/App.tsx

@@ -10,6 +10,7 @@ import InvoiceDetail from "./views/InvoiceDetail";
 import Clients from "./views/Clients";
 import { ToastProvider, useToast } from "./components/ToastProvider";
 import AppSettings from "./views/AppSettings";
+import { requestSettingsTab } from "./lib/settingsTab";
 
 export default function App() {
   return (
@@ -89,6 +90,11 @@ function AppInner() {
     );
   }
 
+  const openIntegrations = () => {
+    requestSettingsTab("integrations");
+    setView("settings");
+  };
+
   const toggleTheme = async () => {
     const next: Settings = { ...settings, theme: settings.theme === "g100" ? "g10" : "g100" };
     setSettings(next);
@@ -115,6 +121,7 @@ function AppInner() {
           <InvoiceHistory
             settings={settings}
             active={view === "invoices"}
+            onOpenSettings={openIntegrations}
             onOpen={(id) => {
               setDetailId(id);
               setView("invoice");
@@ -127,6 +134,7 @@ function AppInner() {
             invoiceId={detailId}
             settings={settings}
             onBack={() => setView("invoices")}
+            onOpenSettings={openIntegrations}
             onDuplicated={(draftId) => {
               setOpenDraftId(draftId);
               setView("new");