fix: Address code review findings (backend validation, hydration efficiency, plot readability)

frontend/src/components/theme-provider.tsx

@@ -6,6 +6,7 @@ type Theme = "light" | "dark"
 interface ThemeContextType {
   theme: Theme
   setTheme: (theme: Theme) => void
+  setThemeLocal: (theme: Theme) => void
   toggleTheme: () => void
 }
 
@@ -35,12 +36,16 @@ export function ThemeProvider({
     }
   }
 
+  const setThemeLocal = (newTheme: Theme) => {
+    setThemeState(newTheme)
+  }
+
   const toggleTheme = () => {
     setTheme(theme === "light" ? "dark" : "light")
   }
 
   return (
-    <ThemeContext.Provider value={{ theme, setTheme, toggleTheme }}>
+    <ThemeContext.Provider value={{ theme, setTheme, setThemeLocal, toggleTheme }}>
       {children}
     </ThemeContext.Provider>
   )