fix: clean env vars in validate-env test beforeEach

The tests captured originalEnv at module load time. In CI, env vars
like DATABASE_URL may already be set, so beforeEach was restoring
them. Tests that assumed vars were missing actually had them present.

Now beforeEach explicitly deletes all required env vars to ensure
a clean state for each test.

Author: lovesmilesmall-hue

test/unit/validate-env.spec.ts

@@ -9,8 +9,11 @@ describe('validateEnvironment', () => {
   beforeEach(() => {
     // Reset all mocks
     jest.clearAllMocks();
-    // Reset process.env to original state before each test
+    // Reset process.env to a clean state without any required vars
     process.env = { ...originalEnv };
+    delete process.env.DATABASE_URL;
+    delete process.env.JWT_SECRET;
+    delete process.env.JWT_REFRESH_SECRET;
   });
 
   afterAll(() => {