refactor: rewrite e2e tests for clarity and correctness

- Fix login test that fails because registration auto-authenticates
- Add modular test structure with clear pass/fail reporting
- Skip moderation tests in CI (detects test-key, no real OpenAI)
- Actually run all test functions (some were defined but never called)
- Early exit on critical failures instead of running useless tests
- Clean up CI workflow env vars

Author: Bentlybro

.github/workflows/e2e-test.yml

@@ -87,8 +87,7 @@ jobs:
     - name: Run core platform tests
       env:
         BASE_URL: http://localhost:6217
-        ADMIN_EMAIL: admin@example.com
-        ADMIN_PASSWORD: admin123
+        OPENAI_API_KEY: "test-key"  # Signals to skip moderation tests
       run: |
         python tests/e2e_test.py