feat: add context menu component and update dropdown, select styles

- Implemented a new ContextMenu component with various subcomponents for better UI interaction.
- Updated DropdownMenu and Select components to include hover effects for improved user experience.
- Enhanced global styles with new CSS variables for better theming and consistency across components.

src/renderer/components/layout/AppShell.tsx

@@ -6,7 +6,7 @@ import {
   ClipboardCheck,
   FolderKanban,
   PanelLeft,
-  ChevronDown,
+  ChevronUp,
 } from 'lucide-react';
 import { trpc } from '@/lib/trpc';
 import {
@@ -61,15 +61,15 @@ export function AppShell({ children }: AppShellProps) {
         {children}
 
         {/* Right-edge vertical 'keep scrolling for AI' affordance (non-interactive) */}
-        <div className="absolute right-0 top-0 bottom-0 flex items-end justify-center pb-8 pointer-events-none select-none">
+        <div className="absolute right-0 top-0 flex items-end justify-center pt-8 pointer-events-none select-none">
           <div className="flex flex-col items-center gap-1.5 pr-2">
+            <ChevronUp size={10} className="text-muted-foreground/30" />
             <span
               className="text-[9px] text-muted-foreground/30 tracking-widest uppercase font-medium"
               style={{ writingMode: 'vertical-rl', transform: 'rotate(180deg)' }}
             >
-              keep scrolling for AI
+              keep scrolling up for AI
             </span>
-            <ChevronDown size={10} className="text-muted-foreground/30" />
           </div>
         </div>
       </SidebarInset>