feat: print-friendly layout + comment count on every post overview

- Hides Header / HeaderOverlay / Footer / TopBanner / Breadcrumbs and
  the comment accordion when printing. Action toolbar already had
  `print:hidden`.
- Adds @media print rules in app.css: 1.5cm page margins, 11pt body,
  forced black-on-white, expand link URLs after anchor text inside
  articles, keep images and headings together at page breaks.
- PostCard now renders the count pill whenever a value is known (incl.
  zero); previously hidden for `count === 0`, so posts whose comments
  are still pending always looked empty.
- Extracts the bulk-fetch helper to `lib/comment-counts.ts`
  (`fetchCommentCounts` + `postSlugForComments`) and uses it from both
  `BlogOverview` and `PostOverviewBlock`. Homepage / any page with a
  post_overview block now shows the badges too — previously only the
  paginated /posts/* routes did.

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

src/routes/post/[slug]/+page.svelte

@@ -165,14 +165,16 @@
 {/if}
 
 {#if data.commentPageId}
-  <Accordion
-    id="comments-section"
-    label={t(data.translations, T.post_comments)}
-    lazy
-    class="mt-6"
-  >
-    <div class="p-8 border border-zinc-200 rounded-lg">
-      <Comments pageId={data.commentPageId} />
-    </div>
-  </Accordion>
+  <div class="print:hidden">
+    <Accordion
+      id="comments-section"
+      label={t(data.translations, T.post_comments)}
+      lazy
+      class="mt-6"
+    >
+      <div class="p-8 border border-zinc-200 rounded-lg">
+        <Comments pageId={data.commentPageId} />
+      </div>
+    </Accordion>
+  </div>
 {/if}