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/lib/settingsTab.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { SETTINGS_TABS, loadSettingsTab, parseSettingsTab, saveSettingsTab } from "./settingsTab";
+import { SETTINGS_TABS, loadSettingsTab, parseSettingsTab, requestSettingsTab, saveSettingsTab } from "./settingsTab";
 
 describe("settings tab persistence", () => {
   it("maps stored ids to indexes and falls back to the first tab", () => {
@@ -14,4 +14,10 @@ describe("settings tab persistence", () => {
     expect(() => saveSettingsTab(2)).not.toThrow();
     expect(() => saveSettingsTab(99)).not.toThrow();
   });
+
+  it("honours a requested tab once, then goes back to the stored one", () => {
+    requestSettingsTab("integrations");
+    expect(loadSettingsTab()).toBe(SETTINGS_TABS.findIndex((t) => t.id === "integrations"));
+    expect(loadSettingsTab()).toBe(0);
+  });
 });