fix(footer): scope lead-paragraph rule to <article> only

Lead-paragraph rule matched footer MarkdownBlocks (copyright line)
and made it 1.25rem. Restrict to article descendants so footer +
sidebar Markdown stay at their natural size.

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

src/app.css

@@ -338,10 +338,11 @@ main ol:not(.not-prose) li {
   border-radius: 2px;
 }
 
-/* Lead-Paragraph: erstes <p> in einem Top-Level MarkdownBlock größer + leichter
-   (Editorial). Bewusst nur via [data-block-type="markdown"] gescopt — sonst
-   würden auch Card-Beschreibungen mit `.markdown` getroffen. */
-[data-block-type="markdown"] .markdown > p:first-child {
+/* Lead-Paragraph: erstes <p> in einem Top-Level MarkdownBlock innerhalb
+   <article> größer + leichter (Editorial). Bewusst auf article gescopt
+   damit weder Cards (.markdown in Callouts) noch Footer-MarkdownBlocks
+   mit Copyright-Text getroffen werden. */
+article [data-block-type="markdown"] .markdown > p:first-child {
   font-size: 1.25rem;
   line-height: 1.55;
   font-weight: 300;
@@ -350,7 +351,7 @@ main ol:not(.not-prose) li {
 }
 
 @media (min-width: 768px) {
-  [data-block-type="markdown"] .markdown > p:first-child {
+  article [data-block-type="markdown"] .markdown > p:first-child {
     font-size: 1.375rem;
   }
 }