feat: migrate web-search to support Tavily alongside Brave Search

[tavily-integrations]

Summary

• Added Tavily as a configurable, parallel search provider in the web_search MCP tool
• Provider is selectable via SEARCH_PROVIDER env var (brave default, tavily option)
• Each provider falls back to the other on failure when both API keys are configured
• Tavily results are normalized to the same output shape (title, url, description) as Brave

Files changed

• tools/web-search/index.ts — Refactored into searchBrave() and searchTavily() functions with shared SearchResult interface, provider routing via SEARCH_PROVIDER env var, and mutual fallback logic
• .env.example — Added TAVILY_API_KEY and SEARCH_PROVIDER documentation
• package.json — Added @tavily/core dependency

Dependency changes

• Added @tavily/core ^0.6.0 to package.json

Environment variable changes

• Added TAVILY_API_KEY — Tavily API key (required when using Tavily provider)
• Added SEARCH_PROVIDER — Optional; 'brave' (default) or 'tavily'

Notes for reviewers

• Existing Brave Search logic is preserved and remains the default provider
• The MCP tool schema and output format are unchanged — this is fully backward compatible
• Tavily r.content field is mapped to description to match the existing output shape

🤖 Generated with Claude Code

Automated Review

• Passed after 3 attempt(s)
• Final review: The implementation is correct and well-structured. Tavily is integrated as a configurable and fallback search provider via the SEARCH_PROVIDER env var. The SDK is used correctly (tavily({ apiKey }), client.search(), mapping r.content → description). The envVars fix correctly removes TAVILY_API_KEY from startup checks, preventing the tool from being skipped for existing Brave-only users. Fallback logic in both directions (Tavily→Brave and Brave→Tavily) is sound. Two minor issues are noted but do not block approval.