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>

eslint.config.js

@@ -0,0 +1,13 @@
+import baseConfig from "@mosaic/config/eslint/base";
+
+export default [
+  ...baseConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json", "./apps/*/tsconfig.json", "./packages/*/tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+];