test: add regression tests for Critical+High FLAWS_REPORT fixes

- Tests caught 2 real bugs:
  - Zod NaN bypass in orders/offers schemas (Number(v) || fallback)
  - invoiceTotalWithVat using Number() on { toNumber() } objects
- 7 new test files covering auth, env, exchange rates, NAS paths,
  schema NaN rejection, invoice VAT calculation, customer validation
- 45 tests passing, build clean

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/__tests__/auth.service.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect, vi } from "vitest";
+import { verifyAccessToken, hashToken } from "../services/auth";
+import jwt from "jsonwebtoken";
+import { config } from "../config/env";
+
+describe("auth service", () => {
+  describe("verifyAccessToken", () => {
+    it("returns null and logs error for invalid JWT", async () => {
+      const consoleSpy = vi
+        .spyOn(console, "error")
+        .mockImplementation(() => {});
+      const result = await verifyAccessToken("invalid-token");
+      expect(result).toBeNull();
+      expect(consoleSpy).toHaveBeenCalled();
+      expect(consoleSpy.mock.calls[0][0]).toMatch(/JWT verification error/);
+      consoleSpy.mockRestore();
+    });
+
+    it("returns null for expired JWT", async () => {
+      const consoleSpy = vi
+        .spyOn(console, "error")
+        .mockImplementation(() => {});
+      const expiredToken = jwt.sign(
+        { sub: 1, username: "test", role: "user" },
+        config.jwt.secret,
+        { expiresIn: -1 },
+      );
+      const result = await verifyAccessToken(expiredToken);
+      expect(result).toBeNull();
+      expect(consoleSpy).toHaveBeenCalled();
+      consoleSpy.mockRestore();
+    });
+  });
+
+  describe("hashToken", () => {
+    it("produces deterministic SHA-256 hex output", () => {
+      const t1 = hashToken("hello");
+      const t2 = hashToken("hello");
+      expect(t1).toBe(t2);
+      expect(t1).toMatch(/^[a-f0-9]{64}$/);
+    });
+
+    it("produces different hashes for different inputs", () => {
+      const t1 = hashToken("a");
+      const t2 = hashToken("b");
+      expect(t1).not.toBe(t2);
+    });
+  });
+});