Prepare SandBase for the official MCP Registry

[denial123789]

Summary

• add the MCP Registry ownership marker (mcpName)
• add schema-valid server.json metadata for the npm stdio package
• describe SandBase as access to 2,000+ AI models and APIs
• bump the package to 0.1.15 so the published npm artifact and Registry metadata can match

Verification

• npm run lint
• npm test (74 tests)
• npm run audit:package
• git diff --check
• official 2025-12-11 MCP server.json schema validation with AJV
• confirmed the public Registry currently has no SandBase entry

Release dependency

Merge alone does not register the server. Publish @sandbaseai/cli@0.1.15 first so npm exposes the matching mcpName, then authenticate mcp-publisher as the SandBase GitHub organization and publish server.json.

Disclosure: I am affiliated with SandBase; this PR was prepared with AI assistance.