feat(#1): Set up monorepo scaffold with pnpm workspaces + TurboRepo

Implements the foundational project structure including:
- pnpm workspaces configuration
- TurboRepo for build orchestration
- NestJS 11.1.12 API (apps/api)
- Next.js 16.1.6 web app (apps/web)
- Shared packages (config, shared, ui)
- TypeScript strict mode configuration
- ESLint + Prettier setup
- Vitest for unit testing (19 passing tests)

Fixes #1

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/ui/src/components/Button.tsx

@@ -0,0 +1,39 @@
+import type { ButtonHTMLAttributes, ReactNode } from "react";
+
+export interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
+  variant?: "primary" | "secondary" | "danger";
+  size?: "sm" | "md" | "lg";
+  children: ReactNode;
+}
+
+export function Button({
+  variant = "primary",
+  size = "md",
+  children,
+  className = "",
+  ...props
+}: ButtonProps) {
+  const baseStyles = "inline-flex items-center justify-center font-medium rounded-md";
+
+  const variantStyles = {
+    primary: "bg-blue-600 text-white hover:bg-blue-700",
+    secondary: "bg-gray-200 text-gray-900 hover:bg-gray-300",
+    danger: "bg-red-600 text-white hover:bg-red-700",
+  };
+
+  const sizeStyles = {
+    sm: "px-3 py-1.5 text-sm",
+    md: "px-4 py-2 text-base",
+    lg: "px-6 py-3 text-lg",
+  };
+
+  const combinedClassName = [baseStyles, variantStyles[variant], sizeStyles[size], className]
+    .filter(Boolean)
+    .join(" ");
+
+  return (
+    <button className={combinedClassName} {...props}>
+      {children}
+    </button>
+  );
+}