Migrate runner lane evidence to FastAPI

[cbusillo]

Summary

• migrate POST /v1/evidence/runner-lane-registration/audits to native FastAPI with shared Pydantic contract coverage
• preserve legacy response/result shape, bearer mutation auth, runner_lane_registration_audit.write authorization, idempotent replay/conflict behavior, and replay-before-store-gate behavior
• update service-boundary and compatibility-retirement docs for the native route

Validation

• uv run python -m unittest tests.test_http_app.FastApiRunnerLaneRegistrationAuditEvidenceStoreGateTests tests.test_http_app.FastApiRunnerLaneRegistrationAuditEvidenceTests tests.test_service.LaunchplaneServiceTests.test_runner_lane_registration_audit_endpoint_writes_record_for_authorized_workflow tests.test_service.LaunchplaneServiceTests.test_runner_lane_registration_audit_endpoint_replays_idempotent_write tests.test_service.LaunchplaneServiceTests.test_runner_lane_registration_audit_endpoint_rejects_unauthorized_workflow tests.test_service.LaunchplaneServiceTests.test_runner_lane_registration_audit_endpoint_rejects_non_launchplane_product
• uv run --extra dev ruff format --check control_plane/http_app.py control_plane/service.py control_plane/contracts/runner_lane_registration_evidence.py tests/test_http_app.py
• uv run --extra dev ruff check control_plane/http_app.py control_plane/service.py control_plane/contracts/runner_lane_registration_evidence.py tests/test_http_app.py
• uv run --extra dev mypy control_plane tests
• uv run --extra dev ruff check .
• uv run python -m unittest
• uv run /Users/cbusillo/Developer/codex-skills/jetbrains-inspection/scripts/jb-inspect.py closeout --repo "$PWD" --scope changed_files
• review agents: code-gpt-5.5, claude-sonnet-4.6, antigravity; no blocking findings

Refs #1322