feat: add sandbase-harness MCP server

[liyangbing]

Adds SandBase Harness as a Developer Tools MCP server.

• Current repository source and Apache-2.0 license
• stdio transport
• Six documented tools: list_agents, create_session, run_session, get_session, list_artifacts, stop_session
• Local/Docker/Kubernetes/self-hosted sandbox support is described in the source repository

Validation performed:

• node scripts/validate-catalog.mjs
• node scripts/generate-readme.mjs
• git diff --check

This is a refreshed submission after the earlier closed PR; the entry uses the current v0.3.8 project metadata.

[liyangbing]

Maintainer verification for the SandBase Harness entry:\n\n- Canonical source: https://github.com/sandbaseai/sandbase-harness\n- Current release: v0.3.8 — https://github.com/sandbaseai/sandbase-harness/releases/tag/v0.3.8\n- MCP bridge and installation reference: https://github.com/sandbaseai/sandbase-harness/blob/main/docs/mcp-server.md\n- The entry is consistent with the documented local-first/self-hosted runtime, MCP tools, sessions, approvals, audit/replay, and sandbox backends.\n- Isolation depends on the selected backend and deployment configuration; inclusion in a directory is not a security certification or endorsement.\n\nI maintain/contribute to the project; this affiliation is disclosed for curator review.