feat: add like count display on homepage and thumbs-up toggle on detail page

- Display like count with thumbs-up emoji on post cards in index.html
- Add clickable like/unlike button with JS fetch on post_detail.html
- Add POST /web/posts/{slug}/like endpoint in web routes for cookie-auth users
- Guests redirected to /auth/dev-login on 401
- Use block extra_js (matching base template) for inline script

app/presentation/templates/pages/index.html

@@ -52,6 +52,9 @@
             <span class="post-card-meta-item" data-testid="post-date-{{ post.id }}">
                 {{ post.created_at.strftime('%B %d, %Y') }}
             </span>
+            <span class="post-card-meta-item" data-testid="like-count-{{ post.id }}">
+                👍 {{ post.like_count }}
+            </span>
         </div>
         
         <div class="post-card-content" data-testid="post-content-preview-{{ post.id }}">