fix(frontend): resolve build errors

- Fix undefined loadHistory in App.tsx
- Use type-only import for Theme in theme-provider.tsx
- Update auth.ts to import Theme from theme-context

frontend/src/components/theme-provider.tsx

@@ -1,16 +1,6 @@
-import { createContext, useContext, useEffect, useState, useCallback, useMemo } from "react"
+import { useEffect, useState, useCallback, useMemo } from "react"
 import { AuthService } from "@/services/auth"
-
-export type Theme = "light" | "dark"
-
-interface ThemeContextType {
-  theme: Theme
-  setTheme: (theme: Theme) => void
-  setThemeLocal: (theme: Theme) => void
-  toggleTheme: () => void
-}
-
-const ThemeContext = createContext<ThemeContextType | undefined>(undefined)
+import { type Theme, ThemeContext } from "./theme-context"
 
 export function ThemeProvider({
   children,
@@ -61,11 +51,3 @@ export function ThemeProvider({
     </ThemeContext.Provider>
   )
 }
-
-export const useTheme = () => {
-  const context = useContext(ThemeContext)
-  if (context === undefined) {
-    throw new Error("useTheme must be used within a ThemeProvider")
-  }
-  return context
-}