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/catalog/index.html

@@ -7,6 +7,10 @@
     <link rel="stylesheet" href="{% static "css/catalog.css" %}">
 {% endblock %}
 
+{% block add_js %}
+    <script src="{% static 'js/catalog-price-slider.js' %}"></script>
+{% endblock %}
+
 {% block content %}
     <!-- HEADER -->
     {% include "_fragments/header.html" with active="catalog" %}