Fix search input text color visibility

- Add search-input class to both desktop and mobile search inputs
- Set dark text color (#212529) for search input visibility
- Add placeholder styling with lighter color (#6c757d)
- Compile SCSS to CSS with new search input styles

Resolves: White text on white background issue in search fields

engine/templates/assets/header.mustache

@@ -8,7 +8,7 @@
         <!-- Desktop search and language -->
         <div class="d-none d-lg-flex ms-auto align-items-center">
             <form class="d-flex me-3" method="GET" action="">
-                <input class="form-control me-2" type="search" name="search" placeholder="{{t_search_placeholder}}" value="{{search_query}}">
+                <input class="form-control me-2 search-input" type="search" name="search" placeholder="{{t_search_placeholder}}" value="{{search_query}}">
                 <button class="btn btn-outline-light" type="submit">{{t_search_button}}</button>
             </form>
             
@@ -43,7 +43,7 @@
     <div class="collapse navbar-collapse d-lg-none" id="mobileSearch">
         <div class="container-fluid px-0">
             <form class="d-flex px-3 pb-3" method="GET" action="">
-                <input class="form-control me-2" type="search" name="search" placeholder="{{t_search_placeholder}}" value="{{search_query}}">
+                <input class="form-control me-2 search-input" type="search" name="search" placeholder="{{t_search_placeholder}}" value="{{search_query}}">
                 <button class="btn btn-outline-light" type="submit">{{t_search_button}}</button>
             </form>
         </div>