feat: implement Figlet, Pastel, and Unit tools with a unified layout

- Add Figlet text converter with font selection and history
- Add Pastel color palette generator and manipulation suite
- Add comprehensive Units converter with category-based logic
- Introduce AppShell with Sidebar and Header for navigation
- Modernize theme system with CSS variables and new animations
- Update project configuration and dependencies

components/layout/SidebarProvider.tsx

@@ -0,0 +1,36 @@
+'use client';
+
+import * as React from 'react';
+
+interface SidebarContextType {
+  isOpen: boolean;
+  isCollapsed: boolean;
+  toggle: () => void;
+  toggleCollapse: () => void;
+  close: () => void;
+}
+
+const SidebarContext = React.createContext<SidebarContextType | undefined>(undefined);
+
+export function SidebarProvider({ children }: { children: React.ReactNode }) {
+  const [isOpen, setIsOpen] = React.useState(false);
+  const [isCollapsed, setIsCollapsed] = React.useState(false);
+
+  const toggle = React.useCallback(() => setIsOpen((prev) => !prev), []);
+  const toggleCollapse = React.useCallback(() => setIsCollapsed((prev) => !prev), []);
+  const close = React.useCallback(() => setIsOpen(false), []);
+
+  return (
+    <SidebarContext.Provider value={{ isOpen, isCollapsed, toggle, toggleCollapse, close }}>
+      {children}
+    </SidebarContext.Provider>
+  );
+}
+
+export function useSidebar() {
+  const context = React.useContext(SidebarContext);
+  if (!context) {
+    throw new Error('useSidebar must be used within a SidebarProvider');
+  }
+  return context;
+}