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 }}">

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 %}

app/presentation/web/routes.py

@@ -24,6 +24,7 @@ from app.application.use_cases import (
     GetPostUseCase,
     ListPostsUseCase,
     PublishPostUseCase,
+    TogglePostLikeUseCase,
     UpdatePostUseCase,
 )
 from app.domain.exceptions import (
@@ -523,6 +524,39 @@ async def delete_post(
     return RedirectResponse(url="/web/", status_code=303)
 
 
+@router.post("/posts/{post_slug}/like")
+async def toggle_like_web(
+    post_slug: str,
+    user: OptionalUserDep,
+    get_use_case: FromDishka[GetPostUseCase],
+    toggle_use_case: FromDishka[TogglePostLikeUseCase],
+) -> dict[str, object]:
+    """Toggle like on a post via web UI.
+
+    Args:
+        post_slug: The URL-friendly slug of the post.
+        user: Current user from cookie or None.
+        get_use_case: Use case for retrieving posts.
+        toggle_use_case: Use case for toggling likes.
+
+    Returns:
+        JSON dict with updated like_count.
+
+    Raises:
+        HTTPException: If post not found or user not authenticated.
+    """
+    if not user:
+        raise HTTPException(status_code=401, detail="Authentication required")
+
+    try:
+        post = await get_use_case.by_slug(post_slug)
+    except NotFoundException:
+        raise HTTPException(status_code=404, detail="Post not found") from None
+
+    result = await toggle_use_case.execute(post.id, user.user_id)
+    return {"like_count": result.like_count}
+
+
 @router.get("/profile", response_class=HTMLResponse)
 async def profile(
     request: Request,