Align native framing with the pre-1.0 transport boundary

[RobLe3]

Summary

• classify native binary framing as experimental evidence rather than an optional stable capability
• keep maintained native TCP explicitly outside the coordinated stable and production baseline
• add a regression guard and run it in the existing profile-fixture contract

Validation

• python3 tools/check_pre1_feature_baseline.py
• python3 tools/test_pre1_feature_baseline.py
• python3 tools/check_native_framing_fixtures.py
• profile fixture contract reached the pre-existing local dependency boundary; the changed checks pass independently

No release, protocol-wire change, runtime default, deployment or native-transport promotion follows.