fix(#410): use toNodeHandler for BetterAuth Express compatibility

BetterAuth expects Web API Request objects (Fetch API standard) with
headers.get(), but NestJS/Express passes IncomingMessage objects with
headers[] property access. Use better-auth/node's toNodeHandler to
properly convert between Express req/res and BetterAuth's Web API handler.

Also fixes vitest SWC config to read the correct tsconfig for NestJS
decorator metadata emission, which was causing DI injection failures
in tests.

Fixes #410

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/auth/auth.controller.spec.ts

@@ -1,15 +1,18 @@
 import { describe, it, expect, beforeEach, vi } from "vitest";
 import { Test, TestingModule } from "@nestjs/testing";
 import type { AuthUser, AuthSession } from "@mosaic/shared";
+import type { Request as ExpressRequest, Response as ExpressResponse } from "express";
 import { AuthController } from "./auth.controller";
 import { AuthService } from "./auth.service";
 
 describe("AuthController", () => {
   let controller: AuthController;
-  let authService: AuthService;
+
+  const mockNodeHandler = vi.fn().mockResolvedValue(undefined);
 
   const mockAuthService = {
     getAuth: vi.fn(),
+    getNodeHandler: vi.fn().mockReturnValue(mockNodeHandler),
   };
 
   beforeEach(async () => {
@@ -24,25 +27,30 @@ describe("AuthController", () => {
     }).compile();
 
     controller = module.get<AuthController>(AuthController);
-    authService = module.get<AuthService>(AuthService);
 
     vi.clearAllMocks();
+
+    // Restore mock implementations after clearAllMocks
+    mockAuthService.getNodeHandler.mockReturnValue(mockNodeHandler);
+    mockNodeHandler.mockResolvedValue(undefined);
   });
 
   describe("handleAuth", () => {
-    it("should call BetterAuth handler", async () => {
-      const mockHandler = vi.fn().mockResolvedValue({ status: 200 });
-      mockAuthService.getAuth.mockReturnValue({ handler: mockHandler });
-
+    it("should delegate to BetterAuth node handler with Express req/res", async () => {
       const mockRequest = {
         method: "GET",
         url: "/auth/session",
-      };
+        headers: {},
+        ip: "127.0.0.1",
+        socket: { remoteAddress: "127.0.0.1" },
+      } as unknown as ExpressRequest;
 
-      await controller.handleAuth(mockRequest as unknown as Request);
+      const mockResponse = {} as unknown as ExpressResponse;
 
-      expect(mockAuthService.getAuth).toHaveBeenCalled();
-      expect(mockHandler).toHaveBeenCalledWith(mockRequest);
+      await controller.handleAuth(mockRequest, mockResponse);
+
+      expect(mockAuthService.getNodeHandler).toHaveBeenCalled();
+      expect(mockNodeHandler).toHaveBeenCalledWith(mockRequest, mockResponse);
     });
   });