feat(blog-i18n): localize blog UI & SEO; add tag pages to sitemap

- Add Messages.meta.blog and text.blog (BlogTexts) to types/messages
  - Update all locales with blog UI strings and meta.blog
  - Localize blog list, tag pages, and article detail (titles, labels, dates)
  - Pass messages to ArticleListItem; TableOfContents supports localized title
  - Use dictionary-based metadata; alternates cover all supported locales
  - Sitemap: include /[lang]/blog/tag/{tag} and set blog list lastModified to newest post
  - JSON-LD: hardcode site URL in getSiteUrl() for consistency

frontend/components/blog/ArticleListItem.tsx

@@ -1,13 +1,15 @@
 import Link from "next/link";
 import Image from "next/image";
 import { type BlogPost } from "@/lib/blog";
+import { Messages } from "@/types/messages";
 
 interface ArticleListItemProps {
   post: BlogPost;
   lang: string;
+  messages: Messages;
 }
 
-export function ArticleListItem({ post, lang }: ArticleListItemProps) {
+export function ArticleListItem({ post, lang, messages }: ArticleListItemProps) {
   return (
     <article className="bg-white rounded-xl shadow-lg hover:shadow-xl transition-shadow overflow-hidden">
       <div className="relative h-80 w-full">
@@ -24,7 +26,11 @@ export function ArticleListItem({ post, lang }: ArticleListItemProps) {
       <div className="p-8">
         <div className="flex items-center gap-4 text-sm text-gray-500 mb-4">
           <time className="font-medium">
-            {new Date(post.frontmatter.date).toLocaleDateString()}
+            {new Date(post.frontmatter.date).toLocaleDateString(lang, {
+              year: "numeric",
+              month: "long",
+              day: "numeric",
+            })}
           </time>
           <span>·</span>
           <div className="flex gap-2 flex-wrap">
@@ -53,7 +59,7 @@ export function ArticleListItem({ post, lang }: ArticleListItemProps) {
             href={`/${lang}/blog/${post.slug}`}
             className="text-blue-600 hover:text-blue-800 font-medium inline-flex items-center text-lg"
           >
-            Read more
+            {messages.text.blog.read_more}
             <svg
               className="w-5 h-5 ml-2"
               viewBox="0 0 24 24"
@@ -71,7 +77,7 @@ export function ArticleListItem({ post, lang }: ArticleListItemProps) {
 
           <div className="flex items-center gap-3">
             <span className="text-sm">
-              by <span className="font-bold">{post.frontmatter.author}</span>
+              {messages.text.blog.by} <span className="font-bold">{post.frontmatter.author}</span>
             </span>
           </div>
         </div>

frontend/components/blog/TableOfContents.tsx

@@ -10,10 +10,12 @@ interface TocItem {
 
 interface TableOfContentsProps {
   content: string;
+  title?: string;
 }
 
 export const TableOfContents: React.FC<TableOfContentsProps> = ({
   content,
+  title = "Table of contents",
 }) => {
   const [activeId, setActiveId] = useState<string>("");
   const [toc, setToc] = useState<TocItem[]>([]);
@@ -110,7 +112,7 @@ export const TableOfContents: React.FC<TableOfContentsProps> = ({
 
   return (
     <nav className="hidden lg:block sticky top-8 p-6 bg-gray-50 rounded-lg max-h-[calc(100vh-4rem)] overflow-y-auto">
-      <h4 className="text-lg font-semibold mb-4">Table of contents</h4>
+      <h4 className="text-lg font-semibold mb-4">{title}</h4>
       <ul className="space-y-2">
         {toc.map((item) => (
           <li