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/Convert.tsx

@@ -0,0 +1,142 @@
+import { useEffect, useRef } from "react";
+import { useTranslation } from "react-i18next";
+import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
+import { useFileState, useFileSelection } from "@app/contexts/FileContext";
+
+import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
+
+import ConvertSettings from "@app/components/tools/convert/ConvertSettings";
+
+import { useConvertParameters } from "@app/hooks/tools/convert/useConvertParameters";
+import { useConvertOperation } from "@app/hooks/tools/convert/useConvertOperation";
+import { BaseToolProps, ToolComponent } from "@app/types/tool";
+
+const Convert = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
+  const { t } = useTranslation();
+  const { selectors } = useFileState();
+  const activeFiles = selectors.getFiles();
+  const { selectedFiles } = useFileSelection();
+  const scrollContainerRef = useRef<HTMLDivElement>(null);
+
+  const convertParams = useConvertParameters();
+  const convertOperation = useConvertOperation();
+
+  const { enabled: endpointEnabled, loading: endpointLoading } = useEndpointEnabled(convertParams.getEndpointName());
+
+  const scrollToBottom = () => {
+    if (scrollContainerRef.current) {
+      scrollContainerRef.current.scrollTo({
+        top: scrollContainerRef.current.scrollHeight,
+        behavior: "smooth",
+      });
+    }
+  };
+
+  const hasFiles = selectedFiles.length > 0;
+  const hasResults = convertOperation.downloadUrl !== null;
+  const settingsCollapsed = hasResults;
+
+  useEffect(() => {
+    if (selectedFiles.length > 0) {
+      convertParams.analyzeFileTypes(selectedFiles);
+    } else {
+      // Only reset when there are no active files at all
+      // If there are active files but no selected files, keep current format (user filtered by format)
+      if (activeFiles.length === 0) {
+        convertParams.resetParameters();
+      }
+    }
+  }, [selectedFiles, activeFiles, convertParams.analyzeFileTypes, convertParams.resetParameters]);
+
+  useEffect(() => {
+    // Only clear results if we're not currently processing and parameters changed
+    if (!convertOperation.isLoading) {
+      convertOperation.resetResults();
+      onPreviewFile?.(null);
+    }
+  }, [convertParams.parameters.fromExtension, convertParams.parameters.toExtension]);
+
+  useEffect(() => {
+    if (hasFiles) {
+      setTimeout(scrollToBottom, 100);
+    }
+  }, [hasFiles]);
+
+  useEffect(() => {
+    if (hasResults) {
+      setTimeout(scrollToBottom, 100);
+    }
+  }, [hasResults]);
+
+  const handleConvert = async () => {
+    try {
+      await convertOperation.executeOperation(convertParams.parameters, selectedFiles);
+      if (convertOperation.files && onComplete) {
+        onComplete(convertOperation.files);
+      }
+    } catch (error) {
+      if (onError) {
+        onError(error instanceof Error ? error.message : "Convert operation failed");
+      }
+    }
+  };
+
+  const handleThumbnailClick = (file: File) => {
+    onPreviewFile?.(file);
+    sessionStorage.setItem("previousMode", "convert");
+  };
+
+  const handleSettingsReset = () => {
+    convertOperation.resetResults();
+    onPreviewFile?.(null);
+  };
+
+  const handleUndo = async () => {
+    await convertOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
+  return createToolFlow({
+    files: {
+      selectedFiles,
+      isCollapsed: hasResults,
+    },
+    steps: [
+      {
+        title: t("convert.settings", "Settings"),
+        isCollapsed: settingsCollapsed,
+        onCollapsedClick: settingsCollapsed ? handleSettingsReset : undefined,
+        content: (
+          <ConvertSettings
+            parameters={convertParams.parameters}
+            onParameterChange={convertParams.updateParameter}
+            getAvailableToExtensions={convertParams.getAvailableToExtensions}
+            selectedFiles={selectedFiles}
+            disabled={endpointLoading}
+          />
+        ),
+      },
+    ],
+    executeButton: {
+      text: t("convert.convertFiles", "Convert Files"),
+      loadingText: t("convert.converting", "Converting..."),
+      onClick: handleConvert,
+      isVisible: !hasResults,
+      disabled: !convertParams.validateParameters() || !hasFiles || !endpointEnabled,
+      testId: "convert-button",
+    },
+    review: {
+      isVisible: hasResults,
+      operation: convertOperation,
+      title: t("convert.conversionResults", "Conversion Results"),
+      onFileClick: handleThumbnailClick,
+      onUndo: handleUndo,
+      testId: "conversion-results",
+    },
+  });
+};
+
+// Static method to get the operation hook for automation
+Convert.tool = () => useConvertOperation;
+
+export default Convert as ToolComponent;