Improves user display in audit log and requests

Uses usernames instead of user IDs in the audit log and
approval request listings to improve readability. If a user
is not found, it displays a truncated version of the user ID.

static/js/index.js

@@ -857,6 +857,10 @@ window.app = Vue.createApp({
       const account = this.accounts.find(a => a.id === accountId)
       return account ? account.name : accountId
     },
+    getUserName(userId) {
+      const user = this.users.find(u => u.user_id === userId)
+      return user ? user.username : userId.substring(0, 16) + '...'
+    },
     async loadReconciliationSummary() {
       if (!this.isSuperUser) return