Add RedReplier plugin

[TarasShyn]

What this PR does

Adds the redreplier plugin. RedReplier: social listening for Grok Build via a skill plus the hosted RedReplier MCP server. Monitor Reddit, Hacker News, X, and Bluesky for keyword mentions of a product, triage AI-scored leads with relevance reasoning and reply suggestions, manage monitored websites and keywords, and configure alert digests.

• Plugin name: redreplier
• Type: remote source
• Source URL + pinned SHA (remote), or vendored path (local): https://github.com/RedReplier/agent.git @ 6e7f15e43ebffdb59ea06550d9f52bff82c6e2a1
• Homepage: https://redreplier.com

Ownership

• I own this plugin or have the right to distribute it.
• The source repo is published under our official org (or I've explained why not below).

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; local plugins include README.md + .grok-plugin/plugin.json.
• License is stated. (MIT, LICENSE in the source repo and license in .claude-plugin/plugin.json.)

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. (No hooks. One remote MCP server, no local processes.)
• Network endpoints this plugin calls (and why):
• https://mcp.redreplier.com/mcp (hosted MCP server, streamable HTTP; every tool call)
• https://ai.redreplier.com/ai-app/api/v1 (REST API used by the skill's CLI script)
• Credentials/permissions it requires (and why):
• REDREPLIER_API_TOKEN env var: a revocable API token the user creates at redreplier.com/api-tokens. Sent as a Bearer header to the two hosts above and nowhere else.

Notes for reviewers

The skill's scripts/redreplier.js is a zero-dependency Node CLI that only calls the RedReplier API. The mcp-server/ directory holds the server source that also runs the hosted endpoint; it is there so directories like Glama can build and score it, and is not executed by the plugin. Keywords and domains are brand-scoped to redreplier only.