feat(client): add shadcn theme

- Added Nix theme
- Defaults to dark mode

Signed-off-by: Noa Virellia <noa@requiem.garden>

client/src/components/theme-provider.tsx

@@ -0,0 +1,53 @@
+import type { Theme } from '@/hooks/useTheme';
+import { useEffect, useState } from 'react';
+import { ThemeProviderContext } from '@/hooks/useTheme';
+
+interface ThemeProviderProps {
+  children: React.ReactNode;
+  defaultTheme?: Theme;
+  storageKey?: string;
+}
+
+export function ThemeProvider({
+  children,
+  defaultTheme = 'dark',
+  storageKey = 'vite-ui-theme',
+  ...props
+}: ThemeProviderProps) {
+  const [theme, setTheme] = useState<Theme>(
+    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme,
+  );
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+
+    root.classList.remove('light', 'dark');
+
+    if (theme === 'system') {
+      const systemTheme = window.matchMedia('(prefers-color-scheme: dark)')
+        .matches
+        ? 'dark'
+        : 'light';
+
+      root.classList.add(systemTheme);
+      return;
+    }
+
+    root.classList.add(theme);
+  }, [theme]);
+
+  // eslint-disable-next-line react/no-unstable-context-value
+  const value = {
+    theme,
+    setTheme: (theme: Theme) => {
+      localStorage.setItem(storageKey, theme);
+      setTheme(theme);
+    },
+  };
+
+  return (
+    <ThemeProviderContext {...props} value={value}>
+      {children}
+    </ThemeProviderContext>
+  );
+}