docs: add MCP server examples

[hsteude]

Summary

• add a non-root GoFetch MCP server example
• add a deliberately simple Markdown Notes server with persistent storage and text search
• publish the custom image through the existing Artifact Registry workflow pattern
• document Lab and external deployment, connection, and cleanup paths

Testing

• formatted and compiled the custom Python server
• linted the workflow and Kubernetes manifests
• clean-deployed both examples in developer1 and observed ToolHive Ready
• verified both servers run non-root with read-only root filesystems
• initialized MCP through the internal Agent Gateway route from a prokube Lab
• listed the Markdown Notes tools and tested save, search, read, and PVC persistence across a Pod restart

Image

• europe-west3-docker.pkg.dev/prokube-internal/prokube-customer/markdown-notes-mcp:latest
• europe-west3-docker.pkg.dev/prokube-internal/prokube-customer/markdown-notes-mcp:commit-39a62f32a266e10fad6c325b474fc5ef74611b19