feat(ui): F1+F2 — component primitives + rebuilt app shell

F1: shadcn-style primitive set in components/ui (Button, Card, Badge, Input,
Switch, Separator, Skeleton, Tooltip, DropdownMenu, Dialog, Sheet, Tabs, Table,
Toast+useToast, ThemeToggle, PageHeader/StatCard/EmptyState) on Radix + cva.

F2: Layout rebuilt on the new system — sidebar with primary nav (lucide icons)
+ favorites/saved-searches/mailbox/smart-folder sections, sticky topbar with
search, sync status, theme toggle, digest toggle, and an account dropdown. All
prior behavior preserved (auth, sync, collapse/section persistence, "/" search
focus). App wrapped in ToastProvider + TooltipProvider. Build green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ui/input.jsx

@@ -0,0 +1,35 @@
+import { forwardRef } from 'react';
+import { cn } from '../../lib/utils.js';
+
+const Input = forwardRef(function Input({ className, type = 'text', ...props }, ref) {
+  return (
+    <input
+      ref={ref}
+      type={type}
+      className={cn(
+        'flex h-9 w-full rounded-md border border-input bg-card px-3 py-1 text-sm shadow-sm transition-colors',
+        'placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:border-ring',
+        'disabled:cursor-not-allowed disabled:opacity-50',
+        className
+      )}
+      {...props}
+    />
+  );
+});
+
+const Textarea = forwardRef(function Textarea({ className, ...props }, ref) {
+  return (
+    <textarea
+      ref={ref}
+      className={cn(
+        'flex min-h-[72px] w-full rounded-md border border-input bg-card px-3 py-2 text-sm shadow-sm transition-colors',
+        'placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:border-ring',
+        'disabled:cursor-not-allowed disabled:opacity-50',
+        className
+      )}
+      {...props}
+    />
+  );
+});
+
+export { Input, Textarea };