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/styles/carbon.scss

@@ -698,3 +698,76 @@ body {
 .voiced-detail__unarchived p {
   margin-bottom: 1rem;
 }
+
+/* Settings, Integrations, ERPNext */
+.voiced-erp__section > h3 {
+  margin-bottom: 0.5rem;
+}
+
+.voiced-erp__fields {
+  display: grid;
+  gap: 1rem;
+  max-width: 40rem;
+  margin-top: 1rem;
+}
+
+.voiced-erp__label {
+  font-size: 0.75rem;
+  color: var(--cds-text-secondary);
+  margin-bottom: 0.25rem;
+}
+
+.voiced-erp__secret > * + * {
+  margin-top: 0.5rem;
+}
+
+.voiced-erp__result > * + * {
+  margin-top: 0.75rem;
+}
+
+.voiced-erp__uoms {
+  border: 0;
+  padding: 0;
+  display: grid;
+  gap: 1rem;
+}
+
+.voiced-erp__uoms legend {
+  font-size: 0.75rem;
+  color: var(--cds-text-secondary);
+}
+
+.voiced-erp__error {
+  color: var(--cds-text-error);
+  font-size: 0.75rem;
+}
+
+/* ERPNext column and bulk-send bar on the invoices list */
+.voiced-history__bulk {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.5rem;
+  margin-bottom: 1rem;
+}
+
+.voiced-erp__results {
+  list-style: none;
+  margin-top: 1rem;
+  max-height: 16rem;
+  overflow: auto;
+}
+
+.voiced-erp__results li {
+  padding: 0.25rem 0;
+  border-bottom: 1px solid var(--cds-border-subtle);
+}
+
+.voiced-erp__panel {
+  border: 1px solid var(--cds-border-subtle);
+  padding: 1rem;
+}
+
+.voiced-erp__panel > * + * {
+  margin-top: 0.75rem;
+}