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/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,