adding today feature on main habit page, show streaks feature on settings page and improved dark mode functionality

src/contexts/ThemeContext.tsx

@@ -0,0 +1,48 @@
+import React, { createContext, useContext, useState, useEffect } from 'react';
+import { Theme, useTheme } from '../styles/theme';
+
+interface ThemeContextType {
+  theme: Theme;
+  isDark: boolean;
+  showStreaks: boolean;
+  toggleDarkMode: () => void;
+  toggleStreaks: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+export const ThemeProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => {
+  const [isDark, setIsDark] = useState(() => localStorage.getItem('darkMode') === 'true');
+  const [showStreaks, setShowStreaks] = useState(() => localStorage.getItem('showStreaks') !== 'false');
+  const theme = useTheme(isDark);
+
+  useEffect(() => {
+    if (isDark) {
+      document.documentElement.classList.add('dark');
+    } else {
+      document.documentElement.classList.remove('dark');
+    }
+    localStorage.setItem('darkMode', isDark.toString());
+  }, [isDark]);
+
+  useEffect(() => {
+    localStorage.setItem('showStreaks', showStreaks.toString());
+  }, [showStreaks]);
+
+  const toggleDarkMode = () => setIsDark(!isDark);
+  const toggleStreaks = () => setShowStreaks(!showStreaks);
+
+  return (
+    <ThemeContext.Provider value={{ theme, isDark, showStreaks, toggleDarkMode, toggleStreaks }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+};
+
+export const useThemeContext = () => {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error('useThemeContext must be used within a ThemeProvider');
+  }
+  return context;
+};