v0.6.0

Matches the version published on npm (stacktree-mcp@0.6.0) and listed in the MCP Server Registry as ee.stacktr/publish.

• Client spaces tools
• Design guide resource
• .mcp.json + .claude-plugin/plugin.json manifests (Grok Build / Claude plugin ecosystems)
• skills/stacktree-publish skill (frontmatter fix so installers parse it)
• Hosted MCP endpoint: https://api.stacktr.ee/mcp