feat: better demo site (#1241)

* demo: add image-gallery post

* demo: change language weight

* demo: add multilanguage about page

* demo: change title and url

* demo: add shortcode documentation with multi-language support

* demo: improve markdown guide post

* demo: improve Math Typesetting post

* demo: rename Markdown Syntax Guide post

* demo: remove emoji support post

* demo: remove placeholder text post

* demo: remove rich-content post

* demo: rename image gallery page bundle

* demo: add multilingual `Documentation` category

* demo: Increase pagination pager size from 3 to 5.

* demo: add multilingual links, search, and archives pages

* demo: remove `ar` from demosite

demo/config/_default/languages.toml

@@ -1,35 +1,27 @@
 [en]
     languageName = "English"
-    title        = "Example Site"
+    title        = "Hugo Theme Stack"
     weight       = 1
     [en.params.sidebar]
-        subtitle = "Example description"
+        subtitle = "Card-style Hugo theme designed for bloggers"
 
 [zh]
     languageName = "简体中文"
-    title        = "演示站点"
+    title        = "Hugo 主题 Stack"
     weight       = 2
     [zh.params.sidebar]
-        subtitle = "演示说明"
+        subtitle = "为博客设计的卡片式 Hugo 主题"
 
 [zh-hant-tw]
     languageName = "正體中文"
-    title        = "演示站點"
-    weight       = 2
+    title        = "Hugo 主題 Stack"
+    weight       = 3
     [zh-hant-tw.params.sidebar]
-        subtitle = "演示說明"
+        subtitle = "為博客設計的卡片式 Hugo 主題"
 
 [ja]
     languageName = "日本語"
-    title        = "サンプルサイト"
-    weight       = 2
+    title        = "Hugo Theme Stack"
+    weight       = 4
     [ja.params.sidebar]
-        subtitle = "サンプル説明"
-
-[ar]
-    languageName      = "عربي"
-    languagedirection = "rtl"
-    title             = "موقع تجريبي"
-    weight            = 3
-    [ar.params.sidebar]
-        subtitle = "وصف تجريبي"
+        subtitle = "ブログ用のカードスタイルの Hugo テーマ"