Add user settings page and PWA install support

- Add profile update, password change, and account deletion endpoints
- Create Settings page with profile editing, password change, and danger zone
- Add Settings link to user dropdown menu in Layout
- Add /settings route to App.tsx
- Add API functions for profile management
- Create PWA manifest.json and add meta tags to index.html

frontend/src/components/Layout.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react'
 import { Link, useLocation, useNavigate } from 'react-router-dom'
-import { Disc3, LayoutDashboard, Fingerprint, Clock, ListMusic, ListPlus, Compass, Lightbulb, Store, Users, ArrowDownCircle, Heart, Crown, Shield, Menu, X, LogOut, User } from 'lucide-react'
+import { Disc3, LayoutDashboard, Fingerprint, Clock, ListMusic, ListPlus, Compass, Lightbulb, Store, Users, ArrowDownCircle, Heart, Crown, Shield, Menu, X, LogOut, User, Settings } from 'lucide-react'
 import { useAuth } from '../lib/auth'
 
 const ADMIN_EMAIL = 'chris.ryan@deepcutsai.com'
@@ -96,6 +96,14 @@ export default function Layout({ children }: { children: React.ReactNode }) {
                         <p className="text-sm font-medium text-charcoal">{user?.name}</p>
                         <p className="text-xs text-charcoal-muted">{user?.email}</p>
                       </div>
+                      <Link
+                        to="/settings"
+                        onClick={() => setUserMenuOpen(false)}
+                        className="w-full flex items-center gap-2 px-4 py-2 text-sm text-charcoal hover:bg-purple-50 transition-colors no-underline"
+                      >
+                        <Settings className="w-4 h-4" />
+                        Settings
+                      </Link>
                       <button
                         onClick={handleLogout}
                         className="w-full flex items-center gap-2 px-4 py-2 text-sm text-red-600 hover:bg-red-50 transition-colors cursor-pointer bg-transparent border-none text-left"