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/middleware/errorHandler.ts

@@ -0,0 +1,47 @@
+import { Request, Response, NextFunction } from 'express';
+import { ZodError } from 'zod';
+import { logger } from '../utils/logger';
+
+export interface AppError extends Error {
+  statusCode?: number;
+  code?: string;
+  details?: unknown;
+}
+
+export function createError(message: string, statusCode: number, code: string): AppError {
+  const err: AppError = new Error(message);
+  err.statusCode = statusCode;
+  err.code = code;
+  return err;
+}
+
+export function errorHandler(
+  err: AppError,
+  _req: Request,
+  res: Response,
+  _next: NextFunction
+): void {
+  const timestamp = new Date().toISOString();
+
+  if (err instanceof ZodError) {
+    res.status(400).json({
+      error: err.errors.map((e) => `${e.path.join('.')}: ${e.message}`).join('; '),
+      code: 'VALIDATION_ERROR',
+      timestamp,
+    });
+    return;
+  }
+
+  const statusCode = err.statusCode ?? 500;
+  const code = err.code ?? 'INTERNAL_ERROR';
+
+  if (statusCode >= 500) {
+    logger.error({ err }, 'Unhandled server error');
+  }
+
+  res.status(statusCode).json({
+    error: statusCode >= 500 ? 'An internal error occurred.' : err.message,
+    code,
+    timestamp,
+  });
+}