Release 2.8.1: consume python-sdk 2.6.7 (settle set held)

[vvillait88]

Summary

Releases agentscore-commerce 2.8.1, consuming the just-published agentscore-py 2.6.7 (the lock now resolves it; the >=2.6.4 floor already allowed it) and publishing the already-merged minor-patch group (#127). The uv.lock own-version is synced to 2.8.1.

The coupled MPP settle set is deliberately HELD at its coordinated-verified versions: pympp 0.10.1, x402 2.20.0 stay put. uv lock --upgrade would move them (to pympp 0.11.0 / x402 2.21.0, dragging eth-rlp/rlp/hexbytes majors), but the registry requires a signing/domain byte-compare plus a live all-rails settle before the settle set moves. That belongs in a dedicated coupled bump, not a routine refresh.

Type of change

• Bug fix (no breaking change)
• New feature (no breaking change)
• Breaking change (existing callers must update)
• Docs, tests, or internal maintenance only

Public API

None. No exported symbols or wire formats changed. The agentscore-py floor is unchanged (>=2.6.4); only the resolved lock version moved.

Test plan

Ran uv run ruff check, uv run ruff format --check, uv run ty check, and uv run pytest: all clean, 1868 passed (4 skipped), 95.37% coverage (above the 95% bar).

Checklist

• Tests cover the new behavior, and the suite passes locally
• Lint, format, and type checks pass
• Docs and README examples updated if the public surface changed
• No secrets, credentials, or personal data in the diff or the tests