feat(pdf): include VAT calculation in stock purchase document

- Added VAT calculation to the stock purchase document PDF, displaying VAT (15%) alongside the subtotal and total.
- Updated the layout to reflect the new totals structure, ensuring consistency with customer PO documents.
- Revised comments for clarity on the handling of total amounts and VAT reconciliation.

src/lib/pdf/stock-purchase-document.tsx

@@ -1,7 +1,7 @@
 import { Document, Page, View, Text, Image, StyleSheet } from "@react-pdf/renderer";
 import type { Letterhead } from "@/lib/letterhead";
 import type { StockPurchase, StockPurchaseItem, Supplier } from "@/lib/types";
-import { formatZAR, formatDateLong } from "./format";
+import { formatZAR, formatDateLong, vatAmount } from "./format";
 import { defaultAccentFor } from "@/lib/letterhead";
 
 /**
@@ -57,14 +57,15 @@ export interface StockPurchaseDocumentProps {
  *     Cost / Line Total). The SKU column is new vs. customer POs —
  *     stock POs reference stock_items by SKU so the supplier can
  *     cross-check the line.
- *   - right-aligned totals (Subtotal + Total)
+ *   - right-aligned totals (Subtotal + VAT (15%) + Total — rule above Total)
  *
  * Intentionally stripped (vs. the customer PO PDF):
  *   - **No Order Ref line** — stock POs have no customer order. The
  *     supplier must NOT learn anything about the end customer. Same
  *     confidentiality rule as customer POs.
- *   - **No banking details / no VAT line** — same rationale as the
- *     customer PO: we pay what the supplier quotes, no markup math.
+ *   - **No banking details** — supplier invoices via the normal
+ *     commercial channel; the PO is an instruction to supply, not
+ *     a payment instruction.
  *
  * The `STK` suffix on the PO number (e.g. `PO26071601STK`) is the
  * in-band signal to the supplier that this is a stock order, not a
@@ -96,11 +97,20 @@ export function StockPurchaseDocument({
       0
     ) * 100
   ) / 100;
-  // Re-use the supplied snapshot if it differs from the live
-  // computation by < 0.01 — caller might have included an explicit
-  // total_amount that we want to honour (e.g. from the regenerate
-  // API where the PO record already has total_amount set).
-  const total = Math.abs(totalAmount - subtotal) < 0.01 ? totalAmount : subtotal;
+  // 15% VAT on top of the supplier-quoted subtotal — same helper the
+  // customer PO and quote PDFs use, so all three documents compute
+  // VAT identically. Total = subtotal + vat, rounded to 2dp so the
+  // line matches the printed figures exactly.
+  //
+  // The `totalAmount` prop is carried for API backwards-compat with
+  // the existing route (the stock_purchases row stores the VAT-ex
+  // subtotal there); we deliberately ignore it for the printed Total
+  // because the office reconciles VAT returns from the printed PDF,
+  // not the stored field. Mirrors the customer PO behaviour
+  // (`PurchaseOrderDocument` does the same).
+  void totalAmount;
+  const vat = vatAmount(subtotal);
+  const totalInclVat = Math.round((subtotal + vat) * 100) / 100;
 
   return (
     <Document
@@ -212,18 +222,25 @@ export function StockPurchaseDocument({
           })}
         </View>
 
-        {/* Totals — just Subtotal + Total. No VAT (we're buying, the
-            supplier's price is what we pay). Rule above Total mirrors
-            the customer-PO totals block so the two feel like siblings. */}
+        {/* Totals — Subtotal + VAT (15%) + rule + Total. Mirrors the
+            customer-PO totals block so the two PDFs feel like
+            siblings when filed side-by-side. `Subtotal` is the VAT-ex
+            sum (stored on `stock_purchases.total_amount`); the printed
+            `Total` is `subtotal × 1.15` — the figure the office uses
+            for budget / VAT-return reconciliation. */}
         <View style={styles.totals}>
           <View style={styles.totalLine}>
             <Text style={styles.totalLabel}>Subtotal:</Text>
             <Text style={styles.totalValue}>{formatZAR(subtotal)}</Text>
           </View>
+          <View style={styles.totalLine}>
+            <Text style={styles.totalLabel}>VAT (15%):</Text>
+            <Text style={styles.totalValue}>{formatZAR(vat)}</Text>
+          </View>
           <View style={styles.totalRule} />
           <View style={styles.totalLine}>
             <Text style={styles.totalFinalLabel}>Total:</Text>
-            <Text style={styles.totalFinalValue}>{formatZAR(total)}</Text>
+            <Text style={styles.totalFinalValue}>{formatZAR(totalInclVat)}</Text>
           </View>
         </View>
       </Page>