feat(blog): comment count badge on post overview

PostCard now shows a small comment-count pill in the top-left of the
image when count > 0. BlogOverview bulk-fetches counts for the visible
posts via the new `/api/comments/counts?ids=…` endpoint and passes
them down. One request per page render, regardless of card count.

- New helper `getCommentCounts()` in `cms.ts`
- `BlogOverview.svelte` derives slugs from posts, fires bulk fetch
  in `$effect`, hands the result map to `PostCard`
- `PostCard.svelte` accepts `commentCount?: number | null`, renders
  pill only when value is a positive number

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/components/PostCard.svelte

@@ -1,4 +1,6 @@
 <script lang="ts">
+  import Icon from "@iconify/svelte";
+  import "$lib/iconify-offline";
   import type { PostEntry } from "$lib/cms";
   import PostMeta from "./PostMeta.svelte";
   import EventBadges from "./EventBadges.svelte";
@@ -15,10 +17,13 @@
     post,
     href,
     tagBase = "/posts/tag",
+    commentCount = null,
   }: {
     post: PostWithImage;
     href: string;
     tagBase?: string;
+    /** Approved comment count. `null` = unknown/loading, hide badge. `0` = also hide. */
+    commentCount?: number | null;
   } = $props();
 
   const rawImg = $derived(post._rawImageUrl);
@@ -89,6 +94,18 @@
         </span>
       </div>
     {/if}
+    {#if commentCount != null && commentCount > 0}
+      <div class="absolute top-2 left-2">
+        <span
+          class="inline-flex items-center gap-1 rounded-full bg-white/90 px-2 py-1 text-[.65rem] font-semibold tabular-nums text-zinc-700 shadow-sm"
+          aria-label="{commentCount} Kommentare"
+          title="{commentCount} Kommentare"
+        >
+          <Icon icon="mdi:comment-outline" class="size-3" />
+          {commentCount}
+        </span>
+      </div>
+    {/if}
   </div>
   <div class="flex-1 flex flex-col justify-start p-4">
     <PostMeta