perf(ui): migrate icons to SVG sprite system

Replace @remixicon/react with a shared Icon component that renders
via <use href> references to a single hidden SVG sprite. This reduces
DOM node count by replacing inline SVGs with lightweight references.

- Create Icon component with sprite injection (packages/ui/src/components/icon/)
- Migrate all 164 files from @remixicon/react to Icon component
- Auto-generate sprite data from remixicon bundle (scripts/generate-icon-sprite.mjs)
- Add bun run icons:generate to package.json
- Move @remixicon/react to devDependencies
- Add icon usage instructions to theme-system skill

packages/ui/src/components/sections/usage/UsageSidebar.tsx

@@ -5,11 +5,11 @@ import { Button } from '@/components/ui/button';
 import { Checkbox } from '@/components/ui/checkbox';
 import { Tooltip, TooltipTrigger, TooltipContent } from '@/components/ui/tooltip';
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select';
+import { Icon } from "@/components/icon/Icon";
 import { cn } from '@/lib/utils';
 import { QUOTA_PROVIDERS, resolveUsageTone } from '@/lib/quota';
 import { useQuotaStore } from '@/stores/useQuotaStore';
 import { updateDesktopSettings } from '@/lib/persistence';
-import { RiRefreshLine } from '@remixicon/react';
 import { useI18n } from '@/lib/i18n';
 
 interface UsageSidebarProps {
@@ -121,7 +121,7 @@ export const UsageSidebar: React.FC<UsageSidebarProps> = ({ onItemSelect }) => {
               title={t('settings.usage.sidebar.actions.refreshTitle')}
               disabled={isLoading}
             >
-              <RiRefreshLine className={cn('h-3.5 w-3.5', isLoading && 'animate-spin')} />
+              <Icon name="refresh" className={cn('h-3.5 w-3.5', isLoading && 'animate-spin')} />
             </Button>
           </div>
         </div>