fix(app): resolve Bucket E.1 — switch to named isAxiosError import

WS-3 session 1b-ii Task 5a (audit Bucket E.1 — 2 items).

EventTabsNav.vue:
- Replaced \`import axios from 'axios'\` with
  \`import { isAxiosError } from 'axios'\` (no other axios.* usage in
  the file).
- Updated both call sites: \`axios.isAxiosError(...)\` → \`isAxiosError(...)\`
  on lines 53 and 76.

Modern axios pattern; resolves the import/no-named-as-default-member
warnings flagged in the WS-3 1b-i audit. No behaviour change — the
named export is the same function.

Note: this commit is split out from the originally-planned grouped
Task 5 commit because the API stream timed out mid-task. E.2-E.5
follow in subsequent commits.

Tests + typecheck verified green.

Lint baseline: 36 → 34.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/app/src/components/events/EventTabsNav.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import axios from 'axios'
+import { isAxiosError } from 'axios'
 import { useEventChildren, useEventDetail, useTransitionEventStatus } from '@/composables/api/useEvents'
 import { dutchPlural } from '@/lib/dutch-plural'
 import { eventStatusLabelNl, transitionVisualKind } from '@/lib/event-status'
@@ -50,7 +50,7 @@ function cancelTransitionConfirm() {
 }
 
 function transition422Message(err: unknown): string {
-  if (!axios.isAxiosError(err))
+  if (!isAxiosError(err))
     return ''
 
   const body = err.response?.data as { message?: string; errors?: string[] } | undefined
@@ -73,7 +73,7 @@ async function confirmTransition() {
     cancelTransitionConfirm()
   }
   catch (err) {
-    if (axios.isAxiosError(err) && err.response?.status === 422) {
+    if (isAxiosError(err) && err.response?.status === 422) {
       const msg = transition422Message(err)
 
       notificationStore.show(msg || 'Status wijzigen is op dit moment niet mogelijk.', 'error')