refactor: simplify KanbanFilters and SourceQuickFilter components

- Removed unused imports and state management for dropdowns, enhancing performance and readability.
- Replaced custom dropdown implementation with a reusable `Dropdown` component for better consistency across the UI.
- Updated button styles and logic for clearer user interaction in the filters.
- Integrated dropdowns into the `SourceQuickFilter` for improved functionality and user experience.

src/components/ui-showcase/UIShowcaseClient.tsx

@@ -9,7 +9,8 @@ import {
   FormsSection,
   NavigationSection,
   FeedbackSection,
-  DataDisplaySection
+  DataDisplaySection,
+  DropdownsSection
 } from './sections';
 
 export function UIShowcaseClient() {
@@ -33,6 +34,7 @@ export function UIShowcaseClient() {
             <ButtonsSection />
             <BadgesSection />
             <CardsSection />
+            <DropdownsSection />
             <FormsSection />
             <NavigationSection />
             <FeedbackSection />