Add upload queue UI with ExifTool metadata preview on pick.

Users can select images within configured limits, see per-row load status, and inspect raw ExifTool output before upload work continues.

frontend/src/components/upload/MetadataInspector.vue

@@ -0,0 +1,40 @@
+<template>
+    <section class="flex min-h-48 flex-col rounded-lg border border-border bg-card" aria-live="polite">
+        <header class="border-b border-border px-4 py-3">
+            <h2 class="text-sm font-medium text-card-foreground">Metadata</h2>
+            <p v-if="fileName" class="mt-0.5 truncate text-xs text-muted-foreground">{{ fileName }}</p>
+        </header>
+
+        <div class="flex flex-1 flex-col p-4">
+            <p v-if="!fileName" class="text-sm text-muted-foreground">Select an image to view its metadata.</p>
+
+            <p v-else-if="entry.status === 'error'" class="text-sm text-destructive">
+                {{ entry.message }}
+            </p>
+
+            <pre
+                v-else-if="entry.status === 'ready'"
+                class="max-h-96 flex-1 overflow-auto rounded-md bg-muted p-3 text-xs leading-relaxed whitespace-pre-wrap text-foreground"
+                >{{ entry.output }}</pre
+            >
+
+            <p v-else class="text-sm text-muted-foreground">{{ entry.message }}</p>
+        </div>
+    </section>
+</template>
+
+<script setup lang="ts">
+import type { PropType } from 'vue';
+import type { MetadataPreviewEntry } from '@/types/metadata/MetadataPreview';
+
+defineProps({
+    fileName: {
+        type: String as PropType<string | null>,
+        required: true
+    },
+    entry: {
+        type: Object as PropType<MetadataPreviewEntry>,
+        required: true
+    }
+});
+</script>