add top navigation with logo upload and about links.

Shared app header in the layout shell and upload main area flex fix for the new chrome.

frontend/src/components/layout/AppHeader.vue

@@ -0,0 +1,47 @@
+<template>
+    <header class="border-b border-border bg-card">
+        <div class="mx-auto flex h-14 max-w-5xl items-center justify-between gap-4 px-4 sm:px-6">
+            <RouterLink
+                :to="{ name: ROUTE_NAMES.Upload }"
+                class="shrink-0 transition-opacity hover:opacity-80"
+            >
+                <img
+                    src="/logo.png"
+                    alt="Private Image"
+                    class="h-8 w-auto sm:h-9"
+                    width="1024"
+                    height="228"
+                    decoding="async"
+                />
+            </RouterLink>
+
+            <nav class="flex items-center gap-1 sm:gap-2">
+                <RouterLink
+                    v-for="item in navItems"
+                    :key="item.name"
+                    :to="{ name: item.name }"
+                    class="rounded-md px-3 py-2 text-sm transition-colors"
+                    :class="
+                        route.name === item.name
+                            ? 'bg-muted font-medium text-foreground'
+                            : 'text-muted-foreground hover:bg-muted/60 hover:text-foreground'
+                    "
+                >
+                    {{ item.label }}
+                </RouterLink>
+            </nav>
+        </div>
+    </header>
+</template>
+
+<script setup lang="ts">
+import { useRoute } from 'vue-router';
+import { ROUTE_NAMES } from '@/consts/routeNames';
+
+const route = useRoute();
+
+const navItems = [
+    { name: ROUTE_NAMES.Upload, label: 'Upload' },
+    { name: ROUTE_NAMES.About, label: 'About' }
+];
+</script>