feat: implement backend API for Pantree Phase 1 MVP

- Project setup: package.json, tsconfig.json, jest.config.js, .env.example
- Config: env.ts, constants.ts (ALLOWED_UNITS, bcrypt rounds, JWT, deletion windows)
- DB: Knex connection, knexfile, migrations 001-006 (users, password_reset_tokens,
  pantry_items, recipes+recipe_ingredients, shopping_lists+items, deleted_records)
- Seeds: 10 seeded recipes with full ingredient lists
- Middleware: JWT authMiddleware (validates token + user existence), errorHandler
- Utils: Pino logger, JWT sign helper, Zod validators for all request shapes
- Services: authService (signup/signin/google/pwd-reset/soft-delete/restore),
  pantryService (CRUD + case-insensitive duplicate guard),
  recipeService (browse+filter+scale), shoppingListService (CRUD+merge logic),
  syncService (delta sync + tombstone cleanup), emailService (SendGrid)
- Routes: /v1/auth, /v1/pantry, /v1/recipes, /v1/shopping-lists, /v1/sync
- App: Express factory (createApp), server entry point
- Jobs: node-cron daily hard-delete + tombstone cleanup
- Tests: validators, utils, auth, pantry, recipes, shopping lists, sync

.env.example

@@ -0,0 +1,21 @@
+# Server
+NODE_ENV=development
+PORT=3000
+
+# Database
+DATABASE_URL=postgresql://user:password@localhost:5432/pantree
+
+# JWT
+JWT_SECRET=change_this_to_a_long_random_secret_at_least_64_chars
+JWT_EXPIRES_IN=24h
+
+# Google OAuth
+GOOGLE_CLIENT_ID=your_google_client_id_here
+
+# SendGrid
+SENDGRID_API_KEY=your_sendgrid_api_key_here
+SENDGRID_FROM_EMAIL=noreply@pantree.app
+
+# App
+FRONTEND_URL=https://pantree.app
+PASSWORD_RESET_URL=https://pantree.app/reset-password