Improve showcase pages: drawers, modals, badges, and Vite caching fix

- DTDrawer: storefront-matching dual-element bevel border, slide-in/out
  animations from correct edge, 99vh height, bold 2em header, box shadow
- DTModal: interactive demos on Bevels page with all 5 mode variants
- Badges: solid color fill with contrasting text (black on dark, white on light)
  instead of transparent fill with colored text
- Animations: add dt-slide-right and dt-slide-left keyframes for drawers
- Bevels page: remove trash "Button Bevels", add interactive modal/drawer
  demos, fix media frame to use real images with proper bevel styling
- Advanced Cards: remove redundant media frame sections, rename "Menu Items"
  to "Buttons", remove DTButton/dt-btn references
- Forms page: rename "Menu Items" to "Buttons"
- Vite config: exclude design system packages from optimizeDeps pre-bundling
  and watch dist directories to prevent stale CSS during development

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/showcase/desktop/src/renderer/pages/FormsPage.tsx

@@ -102,7 +102,7 @@ export function FormsPage() {
         <CodeLabel text=".dt-filter-header | .dt-filter-header.active" />
       </Section>
 
-      <Section title="Menu Items" description="Beveled filter menu items with active state and level indentation.">
+      <Section title="Buttons" description="Beveled buttons with active state, mode colors, and level indentation.">
         <div style={{ maxWidth: 300 }}>
           {['All Products', 'NFC Implants', 'RFID Tags', 'Accessories', 'Lab Products'].map((name, i) => (
             <button