docs: add SandBase Harness sandbox runtime

[liyangbing]

Summary

• add SandBase Harness to the Containers section
• describe its optional Docker/Kubernetes/self-hosted-worker execution backends
• explicitly bound isolation claims to the selected backend and deployment configuration

Verification

• Repository: https://github.com/sandbaseai/sandbase-harness
• Release: https://github.com/sandbaseai/sandbase-harness/releases/tag/v0.3.8
• License: Apache-2.0
• Deployment guide: https://github.com/sandbaseai/sandbase-harness/blob/main/docs/deployment.md

I maintain/contribute to SandBase Harness. This entry does not claim a universal or microVM-level isolation boundary.

[liyangbing]

Maintainer verification for the SandBase Harness sandbox-runtime 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
• Deployment guide: https://github.com/sandbaseai/sandbase-harness/blob/main/docs/deployment.md
• Official MCP installation/configuration: https://github.com/sandbaseai/sandbase-harness/blob/main/docs/mcp-server.md
• The proposed entry accurately describes optional Docker, Kubernetes, and self-hosted worker backends.
• Please retain the explicit qualification that isolation is backend/deployment dependent and is not a universal microVM guarantee.

The runtime also provides persistent sessions, MCP governance, approvals, credentials, artifacts, audit, and replay as documented in the source repository.

[liyangbing]

Closing this duplicate SandBase Harness listing in favor of the newer PR #9, which targets the same directory entry and contains the current verification/disclosure. Please continue review there: #9