fix(agent-tools): bound HTTP asset gateway requests

[RockChinQ]

Summary

• Bound HTTP MCP request bodies and socket read duration; close stalled peers and track active handlers for safe cleanup.
• Add a focused regression for oversized and incomplete HTTP requests.
• Release as SDK 0.6.0b6 for the LangBot 4.11 beta line.

Verification

• Focused regression and MCP bridge tests pass.
• Ruff, formatting, scoped mypy, sdist/wheel build, and installed-wheel smoke pass.
• Full SDK test suite passed before the version-only bump (1958 passed, 1 skipped).

Release note

This is based on the existing 4.11 beta SDK release line (PR #88), not a merge of the unrelated latest SDK main history.