feat: implement new layout components and routing structure

- Added HeaderLayout component for the application header.
- Introduced KeepAliveViewport for managing tab states and rendering.
- Created TabNav for tab navigation with animated indicator.
- Removed old Tabs component in favor of new layout structure.
- Updated routing with AppRouter and defined appTabs for navigation.
- Enhanced theme context to manage dark mode styles.
- Added new UI components: Badge, Button, Separator, and Tabs.
- Refactored pages to utilize new layout components and improve responsiveness.
- Updated global styles for better theming and layout consistency.
- Introduced TypeScript path aliases for cleaner imports.

frontend/src/pages/RagChat/RagChatPage.tsx

@@ -133,7 +133,6 @@ export const RagChatPage: React.FC = () => {
       sessionId,
       abortRef.current.signal,
     );
-  // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [filterRegulationType, sessionId]);
 
   const sendMessage = (text: string) => {
@@ -173,7 +172,7 @@ export const RagChatPage: React.FC = () => {
   };
 
   return (
-    <div style={{ flex: 1, display: 'flex', height: 'calc(100vh - 128px)' }}>
+    <div style={{ flex: 1, display: 'flex', minHeight: 0, height: '100%' }}>
       {/* ── Left: chat panel ─────────────────────────────────── */}
       <div style={{
         flex: '0 0 60%',