Add payments with TDS, invoice detail view and filterable History (Phase E2)

- Migration M8 adds payments (cash, TDS, mode, reference). Payment status is derived, never stored: unpaid, partially paid, paid, or overdue. Overpayment is rejected, TDS counts toward settling, and only issued invoices accept payments. list_invoices and get_invoice carry the paid, TDS and balance summary.
- New invoice detail view: archived-PDF preview, payments list, Record payment modal, Export, Duplicate (as a draft), Re-render and Cancel. An invoice with payments cannot be cancelled until they are deleted.
- History gets search, status, financial-year, month and client filters, sortable columns, pagination, footer totals and an FY summary. Cancelled invoices are excluded from totals. The per-row archive-status calls are gone; archiving is on the detail page.
- Rust tests for payments and the list summary; vitest for fiscal-year, money, filter and duplicate helpers.

PDF output and fingerprint goldens are unchanged. The new UI has not been run in a webview yet.

src/lib/money.ts

@@ -0,0 +1,27 @@
+import { formatAmount } from "./format";
+
+/**
+ * Parses what a person types into an amount field ("1,25,000", "1250.5", "₹ 99.99") into integer paise
+ * without going through floating point. Returns null for anything that is not a plain amount with at
+ * most two decimals; an empty string is 0.
+ */
+export function parseRupeesToPaise(text: string): number | null {
+  const cleaned = text.replace(/[₹,\s]/g, "");
+  if (cleaned === "") return 0;
+  const m = /^(\d+)(?:\.(\d{0,2}))?$/.exec(cleaned);
+  if (!m) return null;
+  const whole = Number(m[1]);
+  const paise = whole * 100 + Number((m[2] ?? "").padEnd(2, "0"));
+  return Number.isSafeInteger(paise) ? paise : null;
+}
+
+/** 123450 -> "1234.50", for filling an amount field. */
+export function paiseToInput(paise: number): string {
+  const p = Math.max(0, Math.round(paise));
+  return `${Math.floor(p / 100)}.${String(p % 100).padStart(2, "0")}`;
+}
+
+/** 123450 -> "₹1,234.50" */
+export function formatPaise(paise: number): string {
+  return `₹${formatAmount(paise / 100)}`;
+}