feat: add purchase invoice batch print page and related components

- Implemented PurchaseInvoiceBatchPrintPage for printing purchase invoices.
- Created InvoicePrintHeader and InvoicePrintFooter components for invoice layout.
- Added invoice layout presets for different styles (Classic, Compact, Modern).
- Developed PurchaseInvoicePaymentDialog for handling payments against invoices.
- Introduced API mocks for company profile and invoice template configuration.
- Added validation functions for company profile and purchase invoices.
- Defined types for company profile, invoice template configuration, and purchase invoices.

Frontend/erp-system/lib/validations/company-profile.ts

@@ -0,0 +1,22 @@
+// Client-side UX validation only — same thin convention as lib/validations/sales.ts.
+
+const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]+$/
+
+export function validateCompanyProfile(input: {
+  legalName: string
+  addressLine1: string
+  city: string
+  country: string
+  phone: string
+  email: string
+}): Record<string, string> {
+  const errors: Record<string, string> = {}
+  if (!input.legalName.trim()) errors.legalName = "Enter the company's legal name"
+  if (!input.addressLine1.trim()) errors.addressLine1 = "Enter an address"
+  if (!input.city.trim()) errors.city = "Enter a city"
+  if (!input.country.trim()) errors.country = "Enter a country"
+  if (!input.phone.trim()) errors.phone = "Enter a phone number"
+  if (!input.email.trim()) errors.email = "Enter an email address"
+  else if (!EMAIL_RE.test(input.email.trim())) errors.email = "Enter a valid email address"
+  return errors
+}

Frontend/erp-system/lib/validations/purchase-invoices.ts

@@ -0,0 +1,21 @@
+// Client-side UX validation only — required fields, format/range checks the browser can
+// already see. Server-authoritative rules (GRN eligibility, vendor match, duplicate vendor
+// invoice numbers) are never re-implemented here. Same pattern as lib/validations/sales.ts.
+
+export function validatePurchaseInvoiceHeader(input: {
+  vendorId: number | null
+  vendorInvoiceNo: string
+  vendorInvoiceDate: string
+  grnIds: number[]
+}): Record<string, string> {
+  const errors: Record<string, string> = {}
+  if (!input.vendorId) errors.vendorId = "Select a vendor"
+  if (!input.vendorInvoiceNo.trim()) errors.vendorInvoiceNo = "Enter the vendor's invoice number"
+  if (!input.vendorInvoiceDate) {
+    errors.vendorInvoiceDate = "Enter the vendor's invoice date"
+  } else if (input.vendorInvoiceDate > new Date().toISOString().slice(0, 10)) {
+    errors.vendorInvoiceDate = "Invoice date cannot be in the future"
+  }
+  if (input.grnIds.length === 0) errors.grnIds = "Select at least one GRN to consolidate"
+  return errors
+}