feat: add monorepo configuration and shared packages structure

Root-level setup:
- package.json with Turborepo scripts
- pnpm-workspace.yaml for workspace management
- turbo.json for build pipeline
- Common config files (.nvmrc, .prettierrc, .editorconfig)

Shared packages (packages/):
- @manacore/shared-types - Common TypeScript types
- @manacore/shared-supabase - Unified Supabase client
- @manacore/shared-utils - Date, string, async utilities
- @manacore/shared-ui - React Native UI components (placeholder)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/shared-utils/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "@manacore/shared-utils",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Shared utility functions for Manacore monorepo",
+  "main": "./src/index.ts",
+  "types": "./src/index.ts",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "scripts": {
+    "type-check": "tsc --noEmit",
+    "clean": "rm -rf dist"
+  },
+  "dependencies": {
+    "date-fns": "^4.1.0"
+  },
+  "devDependencies": {
+    "typescript": "^5.9.2"
+  }
+}