Add a new built-in MCP preset (Slack, Linear, Sentry, or Notion)

[aakashrajput]

What

src/mcp/presets.ts ships 7 built-in MCP server presets (filesystem, github, git, postgres, brave-search, puppeteer, sqlite) enabled via /mcp enable <preset>. Adding a well-known MCP server (e.g. Slack, Linear, Sentry, or Notion) is a self-contained addition.

Where to start

Add a new entry to the MCP_PRESETS array following the existing shape:

{
  id:          "slack",
  name:        "Slack",
  description: "Read channels, post messages, search history",
  envVars:     ["SLACK_BOT_TOKEN"],
  config: {
    command:     "npx",
    args:        ["-y", "@modelcontextprotocol/server-slack"],
    description: "Slack API via MCP — requires SLACK_BOT_TOKEN env var",
  },
},

(Check the actual npm package name for whichever server you pick — some community MCP servers use different install commands than the official @modelcontextprotocol/* scope.)

Acceptance criteria

• New preset appears in /mcp enable <preset> and connects successfully with valid credentials in the environment.
• README's MCP section and the docs site's content/docs/mcp.md mention the new preset.

Why it's a good first issue

Config-only addition, no logic changes, existing presets are the template.

[Ayush7614]

Hi @aakashrajput — PR adding the Slack MCP preset: #51