Migrate from Express 4 to Express 5

- Upgraded express from ^4.22.1 to ^5.2.1
- Added comprehensive Express 5 migration tests with TDD approach
- All 667 tests passing (663 existing + 4 new migration tests)
- No breaking changes detected in the codebase
- Express 5's native async error handling now active
- TypeScript compilation successful with @types/express ^5.0.6

Express 5 features now available:
- Automatic async error catching in route handlers
- Improved performance and stricter path matching
- Default export import style already in use

src/__tests__/express5-migration.test.ts

@@ -0,0 +1,89 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import request from "supertest";
+import express, { Request, Response, NextFunction } from "express";
+import { app } from "../index.js";
+
+describe("Express 5 Migration Tests", () => {
+  describe("Version Check", () => {
+    it("should be running Express 5.x", () => {
+      // This test will fail on Express 4 and pass on Express 5
+      const expressVersion = require('express/package.json').version;
+      expect(expressVersion).toMatch(/^5\./);
+    });
+  });
+
+  describe("Async Error Handling", () => {
+    let testApp: express.Application;
+
+    beforeEach(() => {
+      testApp = express();
+      testApp.use(express.json());
+    });
+
+    it("should automatically catch async errors without explicit error handling (Express 5 feature)", async () => {
+      // Express 5 automatically catches rejected promises in route handlers
+      // This test verifies that behavior
+      let errorHandlerCalled = false;
+      
+      testApp.get("/test-async-error", async (req: Request, res: Response) => {
+        // Deliberately cause an async error without try/catch
+        await new Promise((resolve, reject) => {
+          setTimeout(() => reject(new Error("Async test error")), 1);
+        });
+        res.json({ success: true });
+      });
+
+      // Add error handler
+      testApp.use((err: any, req: Request, res: Response, next: NextFunction) => {
+        errorHandlerCalled = true;
+        res.status(500).json({ error: "Caught async error" });
+      });
+
+      const response = await request(testApp)
+        .get("/test-async-error")
+        .expect(500);
+
+      expect(response.body).toEqual({ error: "Caught async error" });
+      expect(errorHandlerCalled).toBe(true);
+    });
+
+    it("should handle async errors in middleware without explicit error handling", async () => {
+      let errorHandlerCalled = false;
+
+      // Async middleware that throws
+      testApp.use(async (req: Request, res: Response, next: NextFunction) => {
+        await new Promise((resolve, reject) => {
+          setTimeout(() => reject(new Error("Middleware async error")), 1);
+        });
+        next();
+      });
+
+      testApp.get("/test-middleware-error", (req: Request, res: Response) => {
+        res.json({ success: true });
+      });
+
+      // Error handler
+      testApp.use((err: any, req: Request, res: Response, next: NextFunction) => {
+        errorHandlerCalled = true;
+        res.status(500).json({ error: "Middleware error caught" });
+      });
+
+      const response = await request(testApp)
+        .get("/test-middleware-error")
+        .expect(500);
+
+      expect(response.body).toEqual({ error: "Middleware error caught" });
+      expect(errorHandlerCalled).toBe(true);
+    });
+  });
+
+  describe("Express Import Style", () => {
+    it("should support default import syntax (Express 5)", () => {
+      // Express 5 uses default export, Express 4 uses named export
+      // This test verifies we can import express as default export
+      const express = require('express');
+      expect(typeof express).toBe('function');
+      expect(typeof express.default).toBe('undefined'); // Should not need .default
+    });
+  });
+});