feat(accidentForm): sort filtered participants by last and first name

- Enhanced the availableMembers computed property to sort filtered members alphabetically by last name and then by first name, improving the organization of participant lists.

frontend/src/components/AccidentFormDialog.vue

@@ -93,7 +93,18 @@ export default {
             : this.participants)
         : [];
       const participantSet = new Set(participantIds);
-      return this.members.filter(m => participantSet.has(m.id));
+      const filtered = this.members.filter(m => participantSet.has(m.id));
+      // Alphabetisch sortieren nach Nachname, dann Vorname
+      return filtered.sort((a, b) => {
+        const lastNameA = (a.lastName || '').toLowerCase();
+        const lastNameB = (b.lastName || '').toLowerCase();
+        if (lastNameA !== lastNameB) {
+          return lastNameA.localeCompare(lastNameB, 'de');
+        }
+        const firstNameA = (a.firstName || '').toLowerCase();
+        const firstNameB = (b.firstName || '').toLowerCase();
+        return firstNameA.localeCompare(firstNameB, 'de');
+      });
     },
     isValid() {
       return this.localAccident.memberId && this.localAccident.accident && this.localAccident.accident.trim() !== '';