feat: publication management with cover images, PDFs, and fruit images (story #04)

Full CRUD for publications; link fruits to publications; upload per-fruit
PDF descriptions and fruit images stored as BYTEA; fruit detail page shows
publication descriptions and images. ImageOverlayDrawer for cover thumbnail
full-size view.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ImageOverlayDrawer.vue

@@ -0,0 +1,21 @@
+<script setup lang="ts">
+defineProps<{ src: string; alt?: string }>()
+const emit = defineEmits<{ close: [] }>()
+</script>
+
+<template>
+  <div
+    class="fixed inset-0 z-50 flex items-center justify-center bg-black/70"
+    @click.self="emit('close')"
+  >
+    <div class="relative max-h-screen max-w-screen-lg p-4">
+      <button
+        class="absolute right-2 top-2 rounded bg-white/90 px-2 py-1 text-sm font-bold shadow hover:bg-white"
+        @click="emit('close')"
+      >
+        ✕
+      </button>
+      <img :src="src" :alt="alt ?? 'Bild'" class="max-h-[85vh] max-w-full rounded shadow-lg object-contain" />
+    </div>
+  </div>
+</template>