[Good First Issue] Add more MCP servers to the verified catalog

Description

Metaskill maintains a catalog of verified MCP servers in skill/SKILL.md. We'd love to expand it with more useful servers.

Task

Research and add new MCP servers to the catalog. Each entry needs:

• Server name
• npm package name (must be a real, published package)
• Purpose description
• Transport type (stdio/HTTP)

Some candidates to investigate:

• Slack MCP server
• Notion MCP server
• Linear MCP server
• Sentry MCP server
• Supabase MCP server

Requirements

• Package must be real and published on npm or available via URL
• Must actually work with Claude Code's MCP integration
• Update both the catalog in skill/SKILL.md and the README table

Good First Issue

This involves research + editing Markdown files. No complex code changes.