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/post_detail.html

@@ -33,6 +33,13 @@
             {% else %}
             <span class="badge" data-testid="post-detail-status">{{ _('post.status_draft', current_locale) }}</span>
             {% endif %}
+            <span class="post-card-meta-item" data-testid="post-detail-like-count">
+                <button id="like-button" class="btn-like" data-testid="like-button"
+                        data-post-slug="{{ post.slug }}"
+                        data-liked="false">
+                    👍 <span id="like-count">{{ post.like_count }}</span>
+                </button>
+            </span>
         </div>
     </header>
     
@@ -83,3 +90,42 @@
     </footer>
 </article>
 {% endblock %}
+
+{% block extra_js %}
+<script data-testid="like-script">
+document.addEventListener('DOMContentLoaded', function() {
+    var likeButton = document.getElementById('like-button');
+    if (!likeButton) return;
+
+    likeButton.addEventListener('click', function() {
+        var slug = this.getAttribute('data-post-slug');
+        var countSpan = document.getElementById('like-count');
+
+        fetch('/web/posts/' + slug + '/like', {
+            method: 'POST',
+            headers: {
+                'Accept': 'application/json'
+            }
+        })
+        .then(function(response) {
+            if (response.status === 401) {
+                window.location.href = '/auth/dev-login';
+                return;
+            }
+            if (!response.ok) {
+                throw new Error('Like request failed');
+            }
+            return response.json();
+        })
+        .then(function(data) {
+            if (data && data.like_count !== undefined) {
+                countSpan.textContent = data.like_count;
+            }
+        })
+        .catch(function(error) {
+            console.error('Like error:', error);
+        });
+    });
+});
+</script>
+{% endblock %}