feat: монорепо миграция, Discover/SearxNG улучшения

- Миграция на монорепозиторий (apps/frontend, apps/chat-service, etc.)
- Discover: проверка SearxNG, понятное empty state при ненастроенном поиске
- searxng.ts: валидация URL, проверка JSON-ответа, авто-добавление http://
- docker/searxng-config: настройки для JSON API SearxNG

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/frontend/src/components/ui/Select.tsx

@@ -0,0 +1,50 @@
+import { cn } from '@/lib/utils';
+import { Loader2, ChevronDown } from 'lucide-react';
+import { SelectHTMLAttributes, forwardRef } from 'react';
+
+interface SelectProps extends SelectHTMLAttributes<HTMLSelectElement> {
+  options: { value: any; label: string; disabled?: boolean }[];
+  loading?: boolean;
+}
+
+export const Select = forwardRef<HTMLSelectElement, SelectProps>(
+  ({ className, options, loading = false, disabled, ...restProps }, ref) => {
+    return (
+      <div
+        className={cn(
+          'relative inline-flex w-full items-center',
+          disabled && 'opacity-60',
+        )}
+      >
+        <select
+          {...restProps}
+          ref={ref}
+          disabled={disabled || loading}
+          className={cn(
+            'bg-light-secondary dark:bg-dark-secondary px-3 py-2 flex items-center overflow-hidden border border-light-200 dark:border-dark-200 dark:text-white rounded-lg appearance-none w-full pr-10 text-xs lg:text-sm',
+            className,
+          )}
+        >
+          {options.map(({ label, value, disabled: optionDisabled }) => {
+            return (
+              <option key={value} value={value} disabled={optionDisabled}>
+                {label}
+              </option>
+            );
+          })}
+        </select>
+        <span className="pointer-events-none absolute right-3 flex h-4 w-4 items-center justify-center text-black/50 dark:text-white/60">
+          {loading ? (
+            <Loader2 className="h-4 w-4 animate-spin" />
+          ) : (
+            <ChevronDown className="h-4 w-4" />
+          )}
+        </span>
+      </div>
+    );
+  },
+);
+
+Select.displayName = 'Select';
+
+export default Select;