feat: migrate Hugo Bootstrap theme to latest Hugo with Tailwind CSS and refactor codebase

* replace Bootstrap-based styling with Tailwind CSS
* update theme compatibility for latest Hugo version
* refactor templates and partials
* fix outdated code and broken components
* improve project structure and maintainability
* optimize styling and frontend build setup

layouts/404.en.html

@@ -0,0 +1,23 @@
+{{ define "main" }}
+  <section class="section-sm text-center">
+    <div class="container">
+      <div class="row justify-center">
+        <div class="sm:col-10 md:col-8 lg:col-6">
+          <span class="text-[8rem] block font-bold text-text-dark "> 404 </span>
+          <h1 class="h2 mb-4">Page not found</h1>
+          <div class="content">
+            <p>
+              The page you are looking for might have been removed, had its name
+              changed, or is temporarily unavailable.
+            </p>
+          </div>
+          <a
+            href="{{ site.BaseURL | relLangURL }}"
+            class="btn btn-primary mt-8">
+            Back to home
+          </a>
+        </div>
+      </div>
+    </div>
+  </section>
+{{ end }}