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/shared/tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "extends": "@mosaic/config/typescript/library",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src",
+    "module": "CommonJS",
+    "moduleResolution": "node",
+    "lib": ["ES2022", "DOM"]
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist", "**/*.test.ts"]
+}