Add Tavily Tool

Install the pinned mcp-remote bridge in the agent image and register Tavily's remote MCP server for each selected agent group. The MCP server supplies its tool descriptions and input schemas at runtime.

The registered server exposes:

• mcp__tavily__tavily_search
• mcp__tavily__tavily_extract

The registration is provider-agnostic: any provider with MCP support picks it up (Claude, OpenCode, and Codex all do). Groups on the Claude provider already have the built-in WebSearch and WebFetch tools (container/agent-runner/src/providers/claude.ts), so the skill adds the most for groups on other providers, and for Tavily's structured extraction anywhere.

Phase 1: Pre-flight