fix: address critical and major PR review issues

- Lazy-load Recharts via SparklineChart component with React.lazy + Suspense
- Gate mock auth fallback behind VITE_MOCK_AUTH env var in Login and Register
- Add ProtectedRoute component to guard authenticated routes
- Fix touch target size on New Alert button (min-h-10 -> min-h-12)
- Replace invalid safe-area-pb class with pb-[env(safe-area-inset-bottom)]
- Fix theme toggle button touch targets (min-h-10 -> min-h-12)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/components/BottomNav.tsx

@@ -10,7 +10,7 @@ const navItems = [
 
 export function BottomNav() {
   return (
-    <nav className="fixed bottom-0 left-0 right-0 z-50 border-t border-gray-200 bg-white safe-area-pb">
+    <nav className="fixed bottom-0 left-0 right-0 z-50 border-t border-gray-200 bg-white pb-[env(safe-area-inset-bottom)]">
       <div className="mx-auto flex max-w-lg items-center justify-around">
         {navItems.map(({ to, label, icon: Icon }) => (
           <NavLink

src/components/ProtectedRoute.tsx

@@ -0,0 +1,12 @@
+import { Navigate, Outlet } from 'react-router-dom'
+import { useAuthStore } from '../stores/auth.ts'
+
+export function ProtectedRoute() {
+  const isAuthenticated = useAuthStore((s) => s.isAuthenticated)
+
+  if (!isAuthenticated) {
+    return <Navigate to="/login" replace />
+  }
+
+  return <Outlet />
+}

src/components/SparklineChart.tsx

@@ -0,0 +1,33 @@
+import { LineChart, Line, ResponsiveContainer } from 'recharts'
+
+export function SparklineCard({
+  label,
+  data,
+  current,
+}: {
+  label: string
+  data: { date: string; price: number }[]
+  current: string
+}) {
+  return (
+    <div className="flex items-center gap-4 rounded-xl bg-white p-4 shadow-sm">
+      <div className="min-w-0 flex-1">
+        <p className="text-sm font-medium text-gray-900">{label}</p>
+        <p className="text-lg font-bold text-gray-900">{current}</p>
+      </div>
+      <div className="h-10 w-24">
+        <ResponsiveContainer width="100%" height="100%">
+          <LineChart data={data}>
+            <Line
+              type="monotone"
+              dataKey="price"
+              stroke="#1e40af"
+              strokeWidth={2}
+              dot={false}
+            />
+          </LineChart>
+        </ResponsiveContainer>
+      </div>
+    </div>
+  )
+}