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/components/shared/ToolIcon.tsx

@@ -0,0 +1,34 @@
+import React from "react";
+
+interface ToolIconProps {
+  icon: React.ReactNode;
+  opacity?: number;
+  color?: string;
+  marginRight?: string;
+}
+
+/**
+ * Shared icon component for consistent tool icon styling across the application.
+ * Uses the same visual pattern as ToolButton: scaled to 0.8, centered transform, consistent spacing.
+ */
+export const ToolIcon: React.FC<ToolIconProps> = ({
+  icon,
+  opacity = 1,
+  color = "var(--tools-text-and-icon-color)",
+  marginRight = "0.5rem"
+}) => {
+  return (
+    <div
+      className="tool-button-icon"
+      style={{
+        color,
+        marginRight,
+        transform: "scale(0.8)",
+        transformOrigin: "center",
+        opacity
+      }}
+    >
+      {icon}
+    </div>
+  );
+};