feat: Add responsive navigation and theme selection

- Implemented adaptive navigation (Sidebar for wide screens, Bottom Nav for narrow screens)
- Added manual theme selection (Light/Dark/System)
- Added accent color selection
- Created ThemeProvider for dynamic styling
- Added Settings page
- Refactored Profile page with Quick Access links

Fixes #2
Co-Authored-By: Claude <noreply@anthropic.com>

src/components/Navigation.tsx

@@ -0,0 +1,49 @@
+import React from 'react';
+import { NavLink } from 'react-router-dom';
+import { User, Calendar, GraduationCap, MessageSquare, Settings } from 'lucide-react';
+
+const navItems = [
+  { path: '/profile', label: 'Profile', icon: User },
+  { path: '/schedule', label: 'Schedule', icon: Calendar },
+  { path: '/grades', label: 'Grades', icon: GraduationCap },
+  { path: '/messages', label: 'Messages', icon: MessageSquare },
+  { path: '/settings', label: 'Settings', icon: Settings },
+];
+
+export const Navigation: React.FC = () => {
+  return (
+    <>
+      <nav className="navigation-rail">
+        <div style={{ flex: 1, display: 'flex', flexDirection: 'column', gap: '12px' }}>
+          {navItems.map((item) => (
+            <NavLink
+              key={item.path}
+              to={item.path}
+              className={({ isActive }) => `nav-item ${isActive ? 'active' : ''}`}
+            >
+              <div className="nav-item-icon-wrapper">
+                <item.icon size={24} />
+              </div>
+              <span className="nav-item-label">{item.label}</span>
+            </NavLink>
+          ))}
+        </div>
+      </nav>
+
+      <nav className="navigation-bar">
+        {navItems.map((item) => (
+          <NavLink
+            key={item.path}
+            to={item.path}
+            className={({ isActive }) => `nav-item ${isActive ? 'active' : ''}`}
+          >
+            <div className="nav-item-icon-wrapper">
+              <item.icon size={24} />
+            </div>
+            <span className="nav-item-label">{item.label}</span>
+          </NavLink>
+        ))}
+      </nav>
+    </>
+  );
+};