test: use generated BDD test artifacts

[nogates]

Summary

• add a thin pytest-bdd adapter that builds SDK requests from generated language-neutral plans
• route scenario, setup, pagination, and undo requests through generated test-server sessions
• load generated v1/v2 feature trees and provide a standalone run-bdd-tests.sh entrypoint
• keep the legacy pytest-recording path unchanged when generated artifacts are not configured

The generated runner/server data is intentionally not committed. The SDK only consumes artifacts placed in its checkout and has no runtime dependency on the spec repository or openapi-transformer.

Validation

• Action Connection slice: 18 passed, 2 skipped
• current complete generated corpus: 1665 passed, 2852 native-skipped (4517 collected)
• legacy Action Connection replay smoke test: 1 passed
• Python compile check, Ruff 0.1.4 formatting, shell syntax check

Compatibility integration

The openapi-transformer compatibility workflow cherry-picks the single commit from this PR onto Python master, verifies generated client output is unchanged, generates all BDD artifacts from the current spec, and runs the complete generated feature corpus.