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/views/AppSettings.tsx

@@ -41,6 +41,7 @@ import { ImagePicker } from "../components/ImagePicker";
 import { LogoBranding } from "../components/LogoBranding";
 import DataBackupPanel from "../components/DataBackupPanel";
 import DiagnosticsPanel from "../components/DiagnosticsPanel";
+import ErpnextSettingsPanel from "../components/ErpnextSettingsPanel";
 import { FontOverrideTable } from "../components/FontOverrideTable";
 import { useToast } from "../components/ToastProvider";
 import { SETTINGS_TABS, loadSettingsTab, saveSettingsTab } from "../lib/settingsTab";
@@ -159,7 +160,7 @@ export default function AppSettings({
   return (
     <div className="voiced-page">
       <h1 className="voiced-page__title">Settings</h1>
-      <p className="voiced-page__subtitle">Business details, branding, defaults and bank accounts.</p>
+      <p className="voiced-page__subtitle">Business details, branding, defaults, bank accounts and integrations.</p>
 
       <Tabs selectedIndex={tab} onChange={({ selectedIndex }) => selectTab(selectedIndex)}>
         <TabList aria-label="Settings sections" contained scrollIntoView>
@@ -171,6 +172,7 @@ export default function AppSettings({
           <Tab>Templates &amp; export</Tab>
           <Tab>Fonts</Tab>
           <Tab>Data</Tab>
+          <Tab>Integrations</Tab>
         </TabList>
         <TabPanels>
             <TabPanel>
@@ -516,6 +518,9 @@ export default function AppSettings({
             <TabPanel>
               <DataBackupPanel />
             </TabPanel>
+            <TabPanel>
+              <ErpnextSettingsPanel active={tab === SETTINGS_TABS.findIndex((t) => t.id === "integrations")} />
+            </TabPanel>
         </TabPanels>
       </Tabs>