Add featured-post flag, align tool-page connector arrows, misc blog polish

- Posts collection: new "featured" checkbox (Payload) — /blog now prefers
  a manually-featured post over just the most recent one. Query sorts by
  "-featured,-publishedAt" so multiple accidentally-featured posts
  resolve deterministically (most recent among them wins) instead of
  erroring or being ambiguous.
- challenge/page.tsx: step-connector arrow now uses the same
  /icon-arrow-connector.svg asset as todo-cards/newsletter's HowItWorks,
  replacing its own hand-drawn inline SVG.
- todo-cards & newsletter HowItWorks: connector arrows now vertically
  centered on their icon (md:mt-[1.625rem]), matching Challenge's
  margin-based centering technique instead of sitting flush at the row's
  top edge.
- Blog overview: featured card overlaps the header slightly (-mt-8) per
  Figma-inspired refinement, and now also shows the publish date in its
  meta row (previously only the list items did).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/blog/page.tsx

@@ -43,7 +43,10 @@ export default async function BlogOverviewPage() {
         </Reveal>
 
         {featured && (
-          <Reveal delay={0.1} className="w-full px-[var(--layout-padding-x)] pt-10 pb-4">
+          // -mt-8, not pt-10 — pulls the card up to slightly overlap the
+          // hero section's bottom edge instead of sitting flush below it.
+          // relative z-10 keeps it stacked above the hero's own photo.
+          <Reveal delay={0.1} className="relative z-10 w-full px-[var(--layout-padding-x)] -mt-8 pb-4">
             <Link
               href={`/blog/${featured.slug}`}
               className="group grid grid-cols-1 md:grid-cols-2 w-full max-w-[80rem] mx-auto rounded-md overflow-hidden bg-bg-muted transition-transform duration-300 hover:-translate-y-1"
@@ -58,6 +61,8 @@ export default async function BlogOverviewPage() {
                   <span>{featured.category}</span>
                   <span>•</span>
                   <span>{featured.readTime} Min</span>
+                  <span>•</span>
+                  <span className="uppercase">{formatDate(featured.publishedAt)}</span>
                 </div>
                 <p
                   className="font-semibold text-h-section text-text-primary"