feat(P0-001): scaffold monorepo structure

pnpm workspaces, Turborepo, TypeScript strict, ESLint flat config,
Prettier, Vitest, husky + lint-staged. Placeholder packages for all
16 packages + 2 apps + 2 plugins.

Closes #1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/gateway/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "@mosaic/gateway",
+  "version": "0.0.0",
+  "private": true,
+  "main": "dist/main.js",
+  "scripts": {
+    "build": "tsc",
+    "dev": "tsc --watch",
+    "lint": "eslint src",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "@nestjs/common": "^11.0.0",
+    "@nestjs/core": "^11.0.0",
+    "@nestjs/platform-fastify": "^11.0.0",
+    "fastify": "^5.0.0",
+    "reflect-metadata": "^0.2.0",
+    "rxjs": "^7.8.0"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "typescript": "^5.8.0",
+    "vitest": "^2.0.0"
+  }
+}