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/chat/ChatContainer.tsx

@@ -1,5 +1,4 @@
 import React from 'react';
-import { RiArrowLeftLine } from '@remixicon/react';
 import type { Message, Part, Session } from '@opencode-ai/sdk/v2';
 
 import { ChatInput } from './ChatInput';
@@ -19,6 +18,7 @@ import { useChatTurnNavigation } from './hooks/useChatTurnNavigation';
 import { useDeviceInfo } from '@/lib/device';
 import { Button } from '@/components/ui/button';
 import { OverlayScrollbar } from '@/components/ui/OverlayScrollbar';
+import { Icon } from "@/components/icon/Icon";
 import type { PermissionRequest } from '@/types/permission';
 import type { QuestionRequest } from '@/types/question';
 import { cn } from '@/lib/utils';
@@ -521,7 +521,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
                 ? t('chat.container.returnToParent.titleNamed', { title: parentSession.title })
                 : t('chat.container.returnToParent.title')}
         >
-            <RiArrowLeftLine className="h-4 w-4" />
+            <Icon name="arrow-left" className="h-4 w-4" />
             {t('chat.container.returnToParent.label')}
         </Button>
     ) : null;
@@ -657,7 +657,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({ autoOpenDraft = tr
         };
     }, [currentSessionId, isDesktopExpandedInput, navigation, scrollRef]);
 
-
     React.useLayoutEffect(() => {
         const container = scrollRef.current;
         if (!container) return;