feat(01-code-splitting): convert 31+ route components to React.lazy

- Replace all 31+ static route component imports in App.tsx with React.lazy() dynamic imports
- Add LazyLoadingFallback.tsx shared component for Suspense fallback
- Wrap <Routes> with <Suspense> for chunk loading states
- Handle named exports (ImageStudio, VideoStudio, ProductMarketing, StoryProjectList) with .then() wrapper
- Main bundle reduced from 8.42MB to 2.50MB (70% reduction)
- 190+ chunk files created for on-demand loading per route

Closes Phase 1 Plan 01-01

frontend/src/components/shared/LazyLoadingFallback.tsx

@@ -0,0 +1,28 @@
+import React from 'react';
+import { Box, CircularProgress, Typography } from '@mui/material';
+
+interface LazyLoadingFallbackProps {
+  message?: string;
+}
+
+const LazyLoadingFallback: React.FC<LazyLoadingFallbackProps> = ({ 
+  message = 'Loading...' 
+}) => {
+  return (
+    <Box
+      display="flex"
+      flexDirection="column"
+      alignItems="center"
+      justifyContent="center"
+      minHeight="60vh"
+      gap={2}
+    >
+      <CircularProgress size={40} />
+      <Typography variant="body1" color="textSecondary">
+        {message}
+      </Typography>
+    </Box>
+  );
+};
+
+export default LazyLoadingFallback;