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/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "@mosaic/ui",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    },
+    "./components/*": {
+      "types": "./dist/components/*.d.ts",
+      "import": "./dist/components/*.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "dev": "tsc --watch",
+    "lint": "eslint src/",
+    "lint:fix": "eslint src/ --fix",
+    "typecheck": "tsc --noEmit",
+    "clean": "rm -rf dist",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:coverage": "vitest run --coverage"
+  },
+  "dependencies": {
+    "react": "^19.0.0"
+  },
+  "devDependencies": {
+    "@mosaic/config": "workspace:*",
+    "@testing-library/jest-dom": "^6.6.3",
+    "@testing-library/react": "^16.2.0",
+    "@types/react": "^19.0.8",
+    "jsdom": "^26.0.0",
+    "typescript": "^5.8.2",
+    "vitest": "^3.0.8"
+  },
+  "peerDependencies": {
+    "react": "^18.0.0 || ^19.0.0"
+  }
+}

packages/ui/src/components/Button.test.tsx

@@ -0,0 +1,31 @@
+import { describe, expect, it, afterEach } from "vitest";
+import { render, screen, cleanup } from "@testing-library/react";
+import { Button } from "./Button.js";
+
+afterEach(() => {
+  cleanup();
+});
+
+describe("Button", () => {
+  it("should render children", () => {
+    render(<Button>Click me</Button>);
+    expect(screen.getByRole("button")).toHaveTextContent("Click me");
+  });
+
+  it("should apply variant styles", () => {
+    render(<Button variant="danger">Delete</Button>);
+    const button = screen.getByRole("button");
+    expect(button.className).toContain("bg-red-600");
+  });
+
+  it("should apply size styles", () => {
+    render(<Button size="lg">Large Button</Button>);
+    const button = screen.getByRole("button");
+    expect(button.className).toContain("px-6");
+  });
+
+  it("should pass through additional props", () => {
+    render(<Button disabled>Disabled</Button>);
+    expect(screen.getByRole("button")).toBeDisabled();
+  });
+});

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>
+  );
+}

packages/ui/src/index.ts

@@ -0,0 +1,2 @@
+export { Button } from "./components/Button.js";
+export type { ButtonProps } from "./components/Button.js";

packages/ui/tsconfig.json

@@ -0,0 +1,11 @@
+{
+  "extends": "@mosaic/config/typescript/library",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src",
+    "jsx": "react-jsx",
+    "lib": ["DOM", "DOM.Iterable", "ES2022"]
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist", "**/*.test.tsx"]
+}

packages/ui/vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    globals: false,
+    environment: "jsdom",
+    include: ["src/**/*.test.tsx", "src/**/*.test.ts"],
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "json", "html"],
+      exclude: ["node_modules/", "dist/"],
+    },
+    setupFiles: ["./vitest.setup.ts"],
+  },
+});

packages/ui/vitest.setup.ts

@@ -0,0 +1 @@
+import "@testing-library/jest-dom/vitest";