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

src/config/constants.ts

@@ -0,0 +1,18 @@
+export const ALLOWED_UNITS = [
+  'cups', 'tbsp', 'tsp', 'oz', 'fl_oz',
+  'g', 'kg', 'ml', 'l',
+  'pieces', 'slices', 'cloves', 'pinch',
+  'whole', 'can', 'package', 'bunch'
+] as const;
+
+export type AllowedUnit = typeof ALLOWED_UNITS[number];
+
+export const BCRYPT_ROUNDS = 12;
+export const JWT_EXPIRES_IN = '24h';
+export const PASSWORD_RESET_EXPIRES_HOURS = 1;
+export const ACCOUNT_DELETION_DAYS = 15;
+export const TOMBSTONE_RETENTION_DAYS = 30;
+export const MAX_RECIPE_SCALE = 3;
+export const MIN_RECIPE_SCALE = 1;
+export const DEFAULT_PAGE_LIMIT = 20;
+export const MAX_PAGE_LIMIT = 50;