Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/hooks/useSuggestedTools.ts

@@ -0,0 +1,78 @@
+import { useMemo } from 'react';
+import { useNavigationState } from '@app/contexts/NavigationContext';
+import { useToolNavigation } from '@app/hooks/useToolNavigation';
+import { useToolWorkflow } from '@app/contexts/ToolWorkflowContext';
+import { ToolId } from '@app/types/toolId';
+
+// Material UI Icons
+import CompressIcon from '@mui/icons-material/Compress';
+import SwapHorizIcon from '@mui/icons-material/SwapHoriz';
+import CleaningServicesIcon from '@mui/icons-material/CleaningServices';
+import CropIcon from '@mui/icons-material/Crop';
+import TextFieldsIcon from '@mui/icons-material/TextFields';
+
+export interface SuggestedTool {
+  id: ToolId;
+  title: string;
+  icon: React.ComponentType<any>;
+  href: string;
+  onClick: (e: React.MouseEvent) => void;
+}
+
+const ALL_SUGGESTED_TOOLS: Omit<SuggestedTool, 'href' | 'onClick'>[] = [
+  {
+    id: 'compress',
+    title: 'Compress',
+    icon: CompressIcon
+  },
+  {
+    id: 'convert',
+    title: 'Convert',
+    icon: SwapHorizIcon
+  },
+  {
+    id: 'sanitize',
+    title: 'Sanitize',
+    icon: CleaningServicesIcon
+  },
+  {
+    id: 'split',
+    title: 'Split',
+    icon: CropIcon
+  },
+  {
+    id: 'ocr',
+    title: 'OCR',
+    icon: TextFieldsIcon
+  }
+];
+
+export function useSuggestedTools(): SuggestedTool[] {
+  const { selectedTool } = useNavigationState();
+  const { getToolNavigation } = useToolNavigation();
+  const { getSelectedTool } = useToolWorkflow();
+
+  return useMemo(() => {
+    // Filter out the current tool
+    const filteredTools = ALL_SUGGESTED_TOOLS.filter(tool => tool.id !== selectedTool);
+
+    // Add navigation props to each tool
+    return filteredTools.map(tool => {
+      const toolRegistryEntry = getSelectedTool(tool.id);
+      if (!toolRegistryEntry) {
+        // Fallback for tools not in registry
+        return {
+          ...tool,
+          href: `/${tool.id}`,
+          onClick: (e: React.MouseEvent) => { e.preventDefault(); }
+        };
+      }
+      
+      const navProps = getToolNavigation(tool.id, toolRegistryEntry);
+      return {
+        ...tool,
+        ...navProps
+      };
+    });
+  }, [selectedTool, getToolNavigation, getSelectedTool]);
+}