Add HMRC tax reporting to accounts

- Add new HMRC Report tab to accounts reports
- Show total turnover (web + manual sales)
- Calculate cost of goods sold from purchases
- Display gross profit and profit margin
- Show operating expenses breakdown
- Calculate net profit before tax
- Estimate tax liability (19% corporation tax)
- Include HMRC checklist of what needs to be reported
- Help admin prepare for Self Assessment submission

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/admin/accounts/reports/actions.ts

@@ -7,7 +7,7 @@ export async function getReportData() {
   const isAuthenticated = await isAdminAuthenticated();
   if (!isAuthenticated) throw new Error('Unauthorized');
 
-  const [orders, manualSales, expenses] = await Promise.all([
+  const [orders, manualSales, expenses, purchases] = await Promise.all([
     prisma.order.findMany({
       select: { id: true, total: true, createdAt: true },
       orderBy: { createdAt: 'asc' },
@@ -20,7 +20,11 @@ export async function getReportData() {
       select: { id: true, amount: true, date: true, category: true },
       orderBy: { date: 'desc' },
     }),
+    prisma.purchase.findMany({
+      select: { id: true, total: true, purchasedAt: true },
+      orderBy: { purchasedAt: 'desc' },
+    }),
   ]);
 
-  return { orders, manualSales, expenses };
+  return { orders, manualSales, expenses, purchases };
 }