feat: add price filter and dynamic slider to catalog

- Implemented JavaScript-based price slider for catalog filtering
- Updated catalog views to handle min/max price inputs and compute slider bounds
- Enhanced templates (`index.html`, `side-bar.html`) with filtering form and updated URLs
- Added CSS for price slider styling and form layout
- Introduced utility functions for URL building and price parsing
- Expanded tests for price filtering, sliders, and sidebar active states
- Updated context processor and header for dynamic navigation with price filters

templates/_fragments/header.html

@@ -3,7 +3,7 @@
     <div class="container">
         <div class="header-top">
             <div class="logo"><a href="/">SantehRay</a></div>
-            <form action="">
+            <form action="/catalog/" method="get">
                 <div class="search-wrap">
                     <div class="search-select-wrap">
                         <div class="search-category-dropdown" data-category-dropdown>
@@ -67,9 +67,11 @@
                         </div>
                     </div>
                     <label>
-                        <input class="search-input" type="text" placeholder="Кто ищет, тот найдет...">
+                        <input class="search-input" type="text" name="q" value="{{ navigation_search_query }}" placeholder="Кто ищет, тот найдет...">
                     </label>
-                    <button>
+                    <input type="hidden" name="min_price" value="{{ navigation_min_price }}">
+                    <input type="hidden" name="max_price" value="{{ navigation_max_price }}">
+                    <button type="submit" aria-label="Найти товары">
                         <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor"
                              class="bi bi-search" viewBox="0 0 16 16">
                             <path d="M11.742 10.344a6.5 6.5 0 1 0-1.397 1.398h-.001q.044.06.098.115l3.85 3.85a1 1 0 0 0 1.415-1.414l-3.85-3.85a1 1 0 0 0-.115-.1zM12 6.5a5.5 5.5 0 1 1-11 0 5.5 5.5 0 0 1 11 0"></path>