feat: add vendor optional fields and configuration hooks

- Implemented VendorOptionalFields component to handle optional vendor details (mobile, email, address) with validation.
- Created useCustomerConfig hook to load optional customer field settings from Sales configuration.
- Developed useProcurementConfig hook to manage Procurement configuration flags.
- Introduced accessConfigApi for managing access configuration settings.
- Added openingBalancesApi for handling opening balances operations.
- Created procurementConfigApi for managing procurement configuration settings.
- Implemented nav-routes for permission-based routing.
- Developed PDF generation for purchase orders with dynamic vendor and item details.
- Added purchase-order tax helpers for tax calculations and formatting.
- Defined types for opening balances and related operations.

Frontend/erp-system/hooks/use-customer-config.ts

@@ -0,0 +1,63 @@
+"use client"
+
+import { useEffect, useState } from "react"
+
+import { salesConfigApi } from "@/lib/api/sales-config"
+
+/** Which optional customer fields Settings -> Sales Configuration has switched on. */
+export interface CustomerFieldConfig {
+  phone: boolean
+  email: boolean
+  address: boolean
+  city: boolean
+  country: boolean
+  creditLimit: boolean
+  creditDays: boolean
+}
+
+/**
+ * Everything on — the default before this became configurable, and what a screen shows until the real switches arrive
+ * (or if they can't be read). The server refuses a value for a field that is off, so a wrong guess is caught there.
+ */
+export const CUSTOMER_FIELDS_ON: CustomerFieldConfig = {
+  phone: true,
+  email: true,
+  address: true,
+  city: true,
+  country: true,
+  creditLimit: true,
+  creditDays: true,
+}
+
+/** Loads the optional-customer-field switches from the Sales configuration. */
+export function useCustomerConfig(): { fields: CustomerFieldConfig; loaded: boolean } {
+  const [fields, setFields] = useState<CustomerFieldConfig>(CUSTOMER_FIELDS_ON)
+  const [loaded, setLoaded] = useState(false)
+
+  useEffect(() => {
+    let active = true
+    salesConfigApi
+      .get()
+      .then(({ data }) => {
+        if (!active) return
+        setFields({
+          phone: data.customerPhoneEnabled,
+          email: data.customerEmailEnabled,
+          address: data.customerAddressEnabled,
+          city: data.customerCityEnabled,
+          country: data.customerCountryEnabled,
+          creditLimit: data.customerCreditLimitEnabled,
+          creditDays: data.customerCreditDaysEnabled,
+        })
+      })
+      .catch(() => {})
+      .finally(() => {
+        if (active) setLoaded(true)
+      })
+    return () => {
+      active = false
+    }
+  }, [])
+
+  return { fields, loaded }
+}