Set up npm workspaces monorepo with Turborepo and local infra

Postgres and Redis run via docker compose on non-default ports (5447/6380)
to avoid clashing with other local services. React is pinned to a single
version across workspaces because Expo requires it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

package.json

@@ -0,0 +1,31 @@
+{
+  "name": "musicshare",
+  "private": true,
+  "workspaces": [
+    "apps/*",
+    "packages/*"
+  ],
+  "scripts": {
+    "dev": "turbo run dev",
+    "build": "turbo run build",
+    "typecheck": "turbo run typecheck",
+    "infra:up": "docker compose up -d",
+    "infra:down": "docker compose down",
+    "db:generate": "npm run db:generate -w @musicshare/api",
+    "db:migrate": "npm run db:migrate -w @musicshare/api",
+    "mobile": "npm run start -w @musicshare/mobile"
+  },
+  "packageManager": "npm@10.8.1",
+  "engines": {
+    "node": ">=22"
+  },
+  "devDependencies": {
+    "turbo": "^2.11.7",
+    "typescript": "~6.0.3"
+  },
+  "overrides": {
+    "react": "19.2.3",
+    "react-dom": "19.2.3",
+    "@types/react": "~19.2.2"
+  }
+}