feat: implement dark/light mode with system detection

- Install and configure next-themes for theme management
- Add ThemeProvider wrapper component with suppressHydrationWarning
- Define light theme CSS variables (off-white backgrounds, green accents)
- Define dark theme CSS variables (hacker theme: terminal blacks, matrix green)
- Update scrollbar styles for both themes
- Add CRT scanline/glow effects (dark mode only)
- Create ThemeToggle component with system/light/dark cycling
- Add theme toggle to Toolbox sidebar
- Update CandleChart to apply theme-specific colors
- Chart colors update dynamically on theme change
- All components use CSS variables for theme compatibility
- FOUC prevention via next-themes inline script

src/components/ThemeProvider.tsx

@@ -0,0 +1,8 @@
+"use client";
+
+import { ThemeProvider as NextThemesProvider } from "next-themes";
+import { type ThemeProviderProps } from "next-themes/dist/types";
+
+export function ThemeProvider({ children, ...props }: ThemeProviderProps) {
+  return <NextThemesProvider {...props}>{children}</NextThemesProvider>;
+}