docs: add SandBase Harness to runtime security references

[liyangbing]

Summary

• Add SandBase Harness to the provenance, instrumentation, and observability section.
• Describe the MCP bridge, approvals, credential controls, audit/replay, and replaceable sandbox backends.
• Explicitly note that isolation guarantees depend on the selected backend and deployment configuration.

Evidence

• Repository: https://github.com/sandbaseai/sandbase-harness
• Installation and MCP bridge: https://github.com/sandbaseai/sandbase-harness/blob/main/llms-install.md
• Runtime/security documentation: https://github.com/sandbaseai/sandbase-harness/tree/main/docs
• License: Apache-2.0

I maintain/contribute to SandBase Harness and am disclosing that affiliation. This entry does not claim kernel-level isolation or vulnerability scanning; it is focused on runtime governance, credentials, and auditability.

[liyangbing]

Maintainer verification for the SandBase Harness provenance/observability entry:

• Source of truth: https://github.com/sandbaseai/sandbase-harness
• Current release: v0.3.8 — https://github.com/sandbaseai/sandbase-harness/releases/tag/v0.3.8
• Official MCP installation/configuration: https://github.com/sandbaseai/sandbase-harness/blob/main/docs/mcp-server.md
• The entry accurately focuses on the MCP bridge, approvals, credential controls, audit/replay, and replaceable sandbox backends.
• Please retain the explicit boundaries: SandBase Harness does not claim kernel-level isolation or vulnerability scanning, and effective isolation depends on the selected backend and deployment configuration.

The provenance/observability classification is consistent with the repository's documented runtime governance and auditability features.