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/tools/SingleLargePage.tsx

@@ -0,0 +1,44 @@
+import { useTranslation } from "react-i18next";
+import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
+import { useSingleLargePageParameters } from "@app/hooks/tools/singleLargePage/useSingleLargePageParameters";
+import { useSingleLargePageOperation } from "@app/hooks/tools/singleLargePage/useSingleLargePageOperation";
+import { useBaseTool } from "@app/hooks/tools/shared/useBaseTool";
+import { BaseToolProps, ToolComponent } from "@app/types/tool";
+
+const SingleLargePage = (props: BaseToolProps) => {
+  const { t } = useTranslation();
+
+  const base = useBaseTool(
+    'singleLargePage',
+    useSingleLargePageParameters,
+    useSingleLargePageOperation,
+    props
+  );
+
+  return createToolFlow({
+    files: {
+      selectedFiles: base.selectedFiles,
+      isCollapsed: base.hasResults,
+    },
+    steps: [],
+    executeButton: {
+      text: t("pdfToSinglePage.submit", "Convert To Single Page"),
+      isVisible: !base.hasResults,
+      loadingText: t("loading"),
+      onClick: base.handleExecute,
+      disabled: !base.params.validateParameters() || !base.hasFiles || !base.endpointEnabled,
+    },
+    review: {
+      isVisible: base.hasResults,
+      operation: base.operation,
+      title: t("pdfToSinglePage.results.title", "Single Page Results"),
+      onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
+    },
+  });
+};
+
+// Static method to get the operation hook for automation
+SingleLargePage.tool = () => useSingleLargePageOperation;
+
+export default SingleLargePage as ToolComponent;