refactor: install shadcn/ui primitives (button, card, input, textarea, label, tabs, switch, dialog, alert-dialog, badge, separator, sonner)

Pinned the CLI to shadcn@2.3.0 rather than the latest (4.16.0): the
latest generation targets Tailwind v4-only syntax (bare-value parens
like `gap-(--card-spacing)`, the `in-*` variant, `--spacing()`) that
silently fails to compile under this project's Tailwind v3.4.6.
2.3.0 is the last CLI generation producing classic hsl(var(--x))
v3-compatible component output.

Swapped @radix-ui/react-icons for the already-installed lucide-react
in dialog.tsx, and dropped sonner's next-themes dependency (the app
has no dark-mode toggle, so Toaster is hardcoded to theme="light").

Old custom src/components/ui/Button.tsx, Card.tsx, and Field.tsx are
removed here; call sites are updated in the following commits.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/ui/textarea.tsx

@@ -0,0 +1,22 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+const Textarea = React.forwardRef<
+  HTMLTextAreaElement,
+  React.ComponentProps<"textarea">
+>(({ className, ...props }, ref) => {
+  return (
+    <textarea
+      className={cn(
+        "flex min-h-[60px] w-full rounded-md border border-input bg-transparent px-3 py-2 text-base shadow-sm placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50 md:text-sm",
+        className
+      )}
+      ref={ref}
+      {...props}
+    />
+  )
+})
+Textarea.displayName = "Textarea"
+
+export { Textarea }