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/config/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "@mosaic/config",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "exports": {
+    "./typescript/base": "./typescript/base.json",
+    "./typescript/nextjs": "./typescript/nextjs.json",
+    "./typescript/nestjs": "./typescript/nestjs.json",
+    "./typescript/library": "./typescript/library.json",
+    "./eslint/base": "./eslint/base.js",
+    "./eslint/nextjs": "./eslint/nextjs.js",
+    "./eslint/nestjs": "./eslint/nestjs.js",
+    "./prettier": "./prettier/index.js"
+  },
+  "dependencies": {
+    "@eslint/js": "^9.21.0",
+    "@typescript-eslint/eslint-plugin": "^8.26.0",
+    "@typescript-eslint/parser": "^8.26.0",
+    "eslint": "^9.21.0",
+    "eslint-config-prettier": "^10.1.0",
+    "eslint-plugin-prettier": "^5.2.3",
+    "prettier": "^3.5.3",
+    "typescript-eslint": "^8.26.0"
+  },
+  "devDependencies": {
+    "typescript": "^5.8.2"
+  }
+}