Add gurusup plugin

[nchgn]

What this PR does

• Plugin name: gurusup
• Type: remote source
• Source URL + pinned SHA: https://github.com/gurusup/gurusup-brain-plugin.git @ 4709ca345cb55a1fab809b6b53523c5c0600be6e
• Homepage: https://gurusup.com/brain/mcp

Gurusup is a company memory: it answers questions about customers, projects, people and decisions from the sources a team connects (Slack, HubSpot, Notion, uploaded documents and more), with the sources behind each answer. The plugin ships one remote MCP server (gurusup-brain, Streamable HTTP) and one skill (using-brain) that tells the agent to check Gurusup first for company questions.

Ownership

• I own this plugin or have the right to distribute it.
• The source repo is published under our official org (gurusup).

Checklist

• Added/updated exactly one entry in .grok-plugin/marketplace.json (valid JSON, kebab-case name).
• Remote source pins a full 40-char lowercase commit sha, and that commit is public + reachable.
• Regenerated .grok-plugin/plugin-index.json (python3 scripts/generate-plugin-index.py).
• python3 scripts/validate-catalog.py passes locally.
• python3 scripts/generate-plugin-index.py --check passes locally.
• homepage + clear description set.
• License is stated (MIT).

Security

• No curl | bash, remote-code download/exec, or postinstall RCE.
• No reading/exfiltration of secrets, tokens, .env, or env vars.
• Hooks and MCP scope are least-privilege.
• Network endpoints this plugin calls (and why): only https://mcp.brain.gurusup.com/mcp, the hosted Gurusup MCP server. No local code, no hooks, no scripts.
• Credentials/permissions it requires (and why): OAuth 2.1 sign-in with the user's Gurusup account. Answers are limited to what that account can see; the plugin stores no credentials.

Notes for reviewers

Some MCP tools write: add_company_knowledge and skills_publish save content to the company's Gurusup workspace, report_issue and send_feedback send reports to Gurusup, and request_human_info can message or call a teammate when its dispatch flag is set. The same server is listed in the official MCP Registry as com.gurusup/gurusup.