fix(seo): 다국어 URL 구조 개선 - slug suffix 제거 및 404 리다이렉트 추가

EN/JA 포스트 URL에서 -en/-ja suffix를 제거하여 깔끔한 URL 구조로 전환
- /en/2026/02/19/okaibox-dev-diary-day2-en/ → /en/2026/02/19/okaibox-dev-diary-day2/
- 266개 포스트에 slug front matter 추가 및 permalink/redirect_from 설정
- hreflang 태그 로직 단순화 (default.html)
- 포스트 페이지 헤더 언어 전환 시 같은 글의 다른 언어 버전으로 이동 (header.html)
- 본문 내부 링크 159개 수정 (49개 파일)
- 날짜 불일치/크로스 언어 등 34개 추가 리다이렉트 설정
- privacy 페이지 /en/privacy/, /ja/privacy/ 리다이렉트 추가

Author: realcoding2003

_includes/header.html

@@ -53,16 +53,31 @@
             <div class="header-utilities">
                 <!-- 언어 전환 (인라인) -->
                 <div class="language-switcher">
-                    {% for lang in site.languages %}
-                        {% if lang == site.default_lang %}
-                            {% assign lang_url = '/' %}
-                        {% else %}
-                            {% assign lang_url = '/' | append: lang | append: '/' %}
-                        {% endif %}
-                        <a href="{{ lang_url | relative_url }}" class="lang-btn {% if lang == current_lang %}active{% endif %}">
-                            {{ lang | upcase }}
-                        </a>
-                    {% endfor %}
+                    {% if page.layout == "post" %}
+                        {%- assign post_date_path = page.date | date: "/%Y/%m/%d/" -%}
+                        {%- assign post_base_slug = page.slug -%}
+                        {% for lang in site.languages %}
+                            {% if lang == site.default_lang %}
+                                {% assign lang_url = post_date_path | append: post_base_slug | append: '/' %}
+                            {% else %}
+                                {% assign lang_url = '/' | append: lang | append: post_date_path | append: post_base_slug | append: '/' %}
+                            {% endif %}
+                            <a href="{{ lang_url | relative_url }}" class="lang-btn {% if lang == current_lang %}active{% endif %}">
+                                {{ lang | upcase }}
+                            </a>
+                        {% endfor %}
+                    {% else %}
+                        {% for lang in site.languages %}
+                            {% if lang == site.default_lang %}
+                                {% assign lang_url = '/' %}
+                            {% else %}
+                                {% assign lang_url = '/' | append: lang | append: '/' %}
+                            {% endif %}
+                            <a href="{{ lang_url | relative_url }}" class="lang-btn {% if lang == current_lang %}active{% endif %}">
+                                {{ lang | upcase }}
+                            </a>
+                        {% endfor %}
+                    {% endif %}
                 </div>
 
                 <!-- 다크모드 토글 -->

_layouts/default.html

@@ -13,39 +13,22 @@
 
     <!-- 다국어 hreflang 태그 -->
     {% if page.layout == "post" %}
-      {%- assign page_lang = page.lang | default: site.default_lang -%}
-      {%- assign post_slug = page.slug -%}
-      {%- if page_lang == "en" -%}
-        {%- assign slug_end = post_slug.size | minus: 3 -%}
-        {%- assign base_slug = post_slug | slice: 0, slug_end -%}
-      {%- elsif page_lang == "ja" -%}
-        {%- assign slug_end = post_slug.size | minus: 3 -%}
-        {%- assign base_slug = post_slug | slice: 0, slug_end -%}
-      {%- else -%}
-        {%- assign base_slug = post_slug -%}
-      {%- endif -%}
+      {%- assign base_slug = page.slug -%}
       {%- assign date_path = page.date | date: "/%Y/%m/%d/" -%}
       <link rel="alternate" hreflang="ko" href="{{ site.url }}{{ date_path }}{{ base_slug }}/" />
-      <link rel="alternate" hreflang="en" href="{{ site.url }}/en{{ date_path }}{{ base_slug }}-en/" />
-      <link rel="alternate" hreflang="ja" href="{{ site.url }}/ja{{ date_path }}{{ base_slug }}-ja/" />
+      <link rel="alternate" hreflang="en" href="{{ site.url }}/en{{ date_path }}{{ base_slug }}/" />
+      <link rel="alternate" hreflang="ja" href="{{ site.url }}/ja{{ date_path }}{{ base_slug }}/" />
       <link rel="alternate" hreflang="x-default" href="{{ site.url }}{{ date_path }}{{ base_slug }}/" />
     {% else %}
-      {% unless paginator and paginator.page > 1 %}
-        {%- assign base_path = page.url | remove: '/en' | remove: '/ja' -%}
+      {%- assign base_path = page.url | remove: '/en' | remove: '/ja' -%}
         <link rel="alternate" hreflang="ko" href="{{ site.url }}{{ base_path }}" />
         <link rel="alternate" hreflang="x-default" href="{{ site.url }}{{ base_path }}" />
         {% unless page.multilingual == false %}
           <link rel="alternate" hreflang="en" href="{{ site.url }}/en{{ base_path }}" />
           <link rel="alternate" hreflang="ja" href="{{ site.url }}/ja{{ base_path }}" />
         {% endunless %}
-      {% endunless %}
     {% endif %}
 
-    <!-- 페이지네이션 noindex -->
-    {% if paginator and paginator.page > 1 %}
-    <meta name="robots" content="noindex, follow">
-    {% endif %}
-    
     <!-- Favicon -->
     <link rel="icon" type="image/x-icon" href="{{ '/assets/favicons/favicon.ico' | relative_url }}">
     <link rel="apple-touch-icon" sizes="180x180" href="{{ '/assets/favicons/apple-touch-icon.png' | relative_url }}">

_posts/2020-03-15-why-i-use-docker-en.md

@@ -6,10 +6,13 @@ categories: [Development, DevOps]
 tags: [Docker, Container, Deployment, DevEnvironment, DevOps]
 author: "Kevin Park"
 lang: en
+slug: why-i-use-docker
 excerpt: "I switched every project to Docker two years ago. Low barrier to entry, easy deployments... but is it really all upside?"
 permalink: /en/:year/:month/:day/:title/
 redirect_from:
   - /2020/03/15/why-i-use-docker-en/
+  - /en/2020/03/15/why-i-use-docker-en/
+
 ---
 
 # My Honest Review After Using Docker for Every Project for 2 Years

_posts/2020-03-15-why-i-use-docker-ja.md

@@ -6,10 +6,13 @@ categories: [Development, DevOps]
 tags: [Docker, コンテナ, デプロイ, 開発環境, DevOps]
 author: "Kevin Park"
 lang: ja
+slug: why-i-use-docker
 excerpt: "2年前からすべてのプロジェクトをDocker基盤に切り替えました。導入障壁が低くてデプロイも楽ですが、本当にメリットだけでしょうか？"
 permalink: /ja/:year/:month/:day/:title/
 redirect_from:
   - /2020/03/15/why-i-use-docker-ja/
+  - /ja/2020/03/15/why-i-use-docker-ja/
+
 ---
 
 # Dockerを2年間すべてのプロジェクトで使ってみた正直な感想

_posts/2020-03-16-developer-laziness-burnout-en.md

@@ -6,10 +6,13 @@ categories: [Life, DevDiary]
 tags: [Developer, Burnout, Laziness, Growth, Experience]
 author: "Kevin Park"
 lang: en
+slug: developer-laziness-burnout
 excerpt: "I still love coding, but my hands just won't move. The architecture is all planned out in my head, yet execution feels impossible. Am I the only one?"
 permalink: /en/:year/:month/:day/:title/
 redirect_from:
   - /2020/03/16/developer-laziness-burnout-en/
+  - /en/2020/03/16/developer-laziness-burnout-en/
+
 ---
 
 # When Coding Is Fun But Your Hands Won't Move

_posts/2020-03-16-developer-laziness-burnout-ja.md

@@ -6,10 +6,13 @@ categories: [Life, DevDiary]
 tags: [開発者, バーンアウト, 怠惰, 自己成長, 開発経験]
 author: "Kevin Park"
 lang: ja
+slug: developer-laziness-burnout
 excerpt: "開発が嫌いになったわけじゃないのに手が動かない。頭の中では設計が完了しているのに実行できない。これって自分だけでしょうか？"
 permalink: /ja/:year/:month/:day/:title/
 redirect_from:
   - /2020/03/16/developer-laziness-burnout-ja/
+  - /ja/2020/03/16/developer-laziness-burnout-ja/
+
 ---
 
 # 開発は楽しいのに手が動かない

_posts/2020-04-20-cloud-vs-onpremise-server-en.md

@@ -6,10 +6,13 @@ categories: [Development, DevOps]
 tags: [Server, Cloud, AWS, OnPremise, IDC, Migration]
 author: "Kevin Park"
 lang: en
+slug: cloud-vs-onpremise-server
 excerpt: "New projects go to the cloud. Old ones stay on IDC servers. I keep telling myself I'll migrate them... but somehow never do."
 permalink: /en/:year/:month/:day/:title/
 redirect_from:
   - /2020/04/20/cloud-vs-onpremise-server-en/
+  - /en/2020/04/20/cloud-vs-onpremise-server-en/
+
 ---
 
 # The Transition From On-Premise to Cloud

_posts/2020-04-20-cloud-vs-onpremise-server-ja.md

@@ -6,10 +6,13 @@ categories: [Development, DevOps]
 tags: [サーバー, クラウド, AWS, オンプレミス, IDC, マイグレーション]
 author: "Kevin Park"
 lang: ja
+slug: cloud-vs-onpremise-server
 excerpt: "新しいプロジェクトはクラウド、既存のものはIDCそのまま。毎回移行しようと思いつつ応急処置だけして先延ばしにしている。"
 permalink: /ja/:year/:month/:day/:title/
 redirect_from:
   - /2020/04/20/cloud-vs-onpremise-server-ja/
+  - /ja/2020/04/20/cloud-vs-onpremise-server-ja/
+
 ---
 
 # オンプレミスからクラウドへの過渡期

_posts/2020-04-21-mysql-uuid-usage-en.md

@@ -6,10 +6,13 @@ categories: [Development, Database]
 tags: [MySQL, UUID, Security, Database, PHP]
 author: "Kevin Park"
 lang: en
+slug: mysql-uuid-usage
 excerpt: "Using auto_increment PKs directly in URLs gets flagged in every security audit. But replacing all PKs with UUIDs is wildly impractical. Here's the realistic middle ground."
 permalink: /en/:year/:month/:day/:title/
 redirect_from:
   - /2020/04/21/mysql-uuid-usage-en/
+  - /en/2020/04/21/mysql-uuid-usage-en/
+
 ---
 
 # Why You Shouldn't Expose Auto Increment PKs in URLs

_posts/2020-04-21-mysql-uuid-usage-ja.md

@@ -6,10 +6,13 @@ categories: [Development, Database]
 tags: [MySQL, UUID, セキュリティ, データベース, PHP]
 author: "Kevin Park"
 lang: ja
+slug: mysql-uuid-usage
 excerpt: "auto_incrementのPKをそのままURLに使うと、セキュリティ監査で毎回指摘される。かといってPKを全部UUIDに変えるのは非効率すぎる。現実的な妥協案をまとめました。"
 permalink: /ja/:year/:month/:day/:title/
 redirect_from:
   - /2020/04/21/mysql-uuid-usage-ja/
+  - /ja/2020/04/21/mysql-uuid-usage-ja/
+
 ---
 
 # Auto Increment PKをURLに露出してはいけない理由