feat(post-card): PostEmptyThumbs — dashed-border placeholder shown in PostCard's hero slot when post has zero linked images

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/posts/PostEmptyThumbs.vue

@@ -0,0 +1,35 @@
+<template>
+  <div class="fc-post-empty">
+    <v-icon size="48" class="fc-post-empty__icon">mdi-image-off-outline</v-icon>
+    <div class="fc-post-empty__text">No images attached to this post</div>
+  </div>
+</template>
+
+<script setup>
+// No props — pure presentational placeholder.
+</script>
+
+<style scoped>
+.fc-post-empty {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 12px;
+  padding: 32px 16px;
+  border: 1px dashed rgb(var(--v-theme-on-surface-variant));
+  border-radius: 8px;
+  background: rgba(20, 23, 26, 0.3);
+  width: 100%;
+  height: 100%;
+  min-height: 200px;
+}
+.fc-post-empty__icon {
+  color: rgb(var(--v-theme-on-surface-variant));
+  opacity: 0.6;
+}
+.fc-post-empty__text {
+  color: rgb(var(--v-theme-on-surface-variant));
+  font-size: 0.9rem;
+}
+</style>