feature(HeaderNav): Add BGv2 to main API versions list

- Add 'BGv2' to mainVersions array in HeaderNav component
- Position BGv2 after BGv1.3 in the version list for logical ordering
- Ensures BGv2 is displayed as a primary version option in the navigation menu

Author: hongwei1

src/components/HeaderNav.vue

@@ -64,7 +64,7 @@ const combinedMessageDocs = computed(() => {
 const debugMenuItems = ref(['/debug/providers-status', '/debug/oidc'])
 
 // Split versions into main and other
-const mainVersions = ['BGv1.3', 'OBPv5.1.0', 'OBPv6.0.0', 'UKv3.1', 'dynamic-endpoints', 'dynamic-entities', 'OBPdynamic-endpoint', 'OBPdynamic-entity']
+const mainVersions = ['BGv1.3', 'BGv2', 'OBPv5.1.0', 'OBPv6.0.0', 'UKv3.1', 'dynamic-endpoints', 'dynamic-entities', 'OBPdynamic-endpoint', 'OBPdynamic-entity']
 const sortedVersions = computed(() => {
   const all = obpApiVersions.value || []
   console.log('All available versions:', all)