Add live interop test for OSLC-RM and OSLC-QM adapters

[mzargham]

Today tests/integration/oslc-roundtrip/
runs only against local fixtures (canonical W3C/OASIS + sanitized
vendor samples in examples/oslc-fixtures/). No vendor divergence
surfaces from those.

Blocked on flexo-rtm-research#23
test-point decision (Eclipse Lyo refimpl, vendor trial, or
project-hosted server).

Acceptance

Once the test point is designated:

• Add tests/integration/oslc-roundtrip/test_live_smoke.py,
  @pytest.mark.live, env-driven (OSLC_RM_URL + OSLC_RM_TOKEN).
• Round-trip a real oslc_rm:Requirement via the adapter (create,
  GET, parse, modify, PUT with If-Match, GET again, asserting
  Layer-A faithfulness end-to-end).
• Sister test for OSLC-QM (oslc_qm:TestCase).
• Update tests/conftest.py to auto-skip on absent env vars (same
  shape as the existing FLEXO_TOKEN skip).