Refactor saveMember function to enhance duplicate member handling, allowing updates to existing duplicates and improving error handling for member existence checks.

server/utils/members.js

@@ -244,7 +244,7 @@ export async function saveMember(memberData) {
   if (memberData.id) {
     // Update existing manual member if present.
     // If the ID belongs to a login-only member shown in the merged list,
-    // create a manual overlay with the same ID so editable fields can be stored.
+    // update an existing manual duplicate or create a manual overlay.
     const index = members.findIndex(m => m.id === memberData.id)
     const duplicate = findDuplicateMember(
       members.filter(m => m.id !== memberData.id),
@@ -253,12 +253,19 @@ export async function saveMember(memberData) {
       memberData.geburtsdatum
     )
 
-    if (duplicate) {
+    if (duplicate && index !== -1) {
       throw new Error('Ein Mitglied mit diesem Namen und Geburtsdatum existiert bereits.')
     }
 
     if (index !== -1) {
       members[index] = { ...members[index], ...memberData }
+    } else if (duplicate) {
+      const duplicateIndex = members.findIndex(m => m.id === duplicate.id)
+      members[duplicateIndex] = {
+        ...members[duplicateIndex],
+        ...memberData,
+        id: members[duplicateIndex].id
+      }
     } else {
       members.push({
         ...memberData,