fix: move impersonation banner inside layout content flow

Replace position:fixed VSystemBar + fragile :deep() CSS overrides
with a normal-flow div inside the Vuexy content area. The banner
renders in VerticalNavLayout's default slot (layout-page-content)
so it sits naturally below the navbar without fighting the layout
system. Sidebar and navbar are no longer affected.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/app/src/components/platform/ImpersonationBanner.vue

@@ -62,12 +62,9 @@ onUnmounted(() => {
 </script>
 
 <template>
-  <VSystemBar
+  <div
     v-if="impersonationStore.isImpersonating"
-    color="warning"
-    height="48"
-    style="z-index: 9999; position: fixed; top: 0; left: 0; right: 0;"
-    class="px-4"
+    class="impersonation-banner d-flex align-center px-4"
   >
     <VIcon
       icon="tabler-user-search"
@@ -93,15 +90,20 @@ onUnmounted(() => {
       variant="elevated"
       color="white"
       class="text-warning"
+      prepend-icon="tabler-arrow-back"
       :loading="isStopping"
       @click="handleStop"
     >
-      <VIcon
-        icon="tabler-arrow-back"
-        size="16"
-        class="me-1"
-      />
       Terug naar admin
     </VBtn>
-  </VSystemBar>
+  </div>
 </template>
+
+<style scoped>
+.impersonation-banner {
+  background: rgb(var(--v-theme-warning));
+  color: rgb(var(--v-theme-on-warning));
+  block-size: 48px;
+  inline-size: 100%;
+}
+</style>