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/RainbowThemeProvider.tsx

@@ -0,0 +1,60 @@
+import { createContext, useContext, ReactNode } from 'react';
+import { MantineProvider } from '@mantine/core';
+import { useRainbowTheme } from '@app/hooks/useRainbowTheme';
+import { mantineTheme } from '@app/theme/mantineTheme';
+import rainbowStyles from '@app/styles/rainbow.module.css';
+import { ToastProvider } from '@app/components/toast';
+import ToastRenderer from '@app/components/toast/ToastRenderer';
+import { ToastPortalBinder } from '@app/components/toast';
+import type { ThemeMode } from '@app/constants/theme';
+
+interface RainbowThemeContextType {
+  themeMode: ThemeMode;
+  isRainbowMode: boolean;
+  isToggleDisabled: boolean;
+  toggleTheme: () => void;
+  activateRainbow: () => void;
+  deactivateRainbow: () => void;
+}
+
+const RainbowThemeContext = createContext<RainbowThemeContextType | null>(null);
+
+export function useRainbowThemeContext() {
+  const context = useContext(RainbowThemeContext);
+  if (!context) {
+    throw new Error('useRainbowThemeContext must be used within RainbowThemeProvider');
+  }
+  return context;
+}
+
+interface RainbowThemeProviderProps {
+  children: ReactNode;
+}
+
+export function RainbowThemeProvider({ children }: RainbowThemeProviderProps) {
+  const rainbowTheme = useRainbowTheme();
+
+  // Determine the Mantine color scheme
+  const mantineColorScheme = rainbowTheme.themeMode === 'rainbow' ? 'dark' : rainbowTheme.themeMode;
+
+  return (
+    <RainbowThemeContext.Provider value={rainbowTheme}>
+      <MantineProvider
+        theme={mantineTheme}
+        defaultColorScheme={mantineColorScheme}
+        forceColorScheme={mantineColorScheme}
+      >
+        <div
+          className={rainbowTheme.isRainbowMode ? rainbowStyles.rainbowMode : ''}
+          style={{ minHeight: '100vh' }}
+        >
+          <ToastProvider>
+            <ToastPortalBinder />
+            {children}
+            <ToastRenderer />
+          </ToastProvider>
+        </div>
+      </MantineProvider>
+    </RainbowThemeContext.Provider>
+  );
+}