Feat: Add unified web search and fetch tool - #343

Summary

Adds web_search_fetch_exa, a unified MCP tool that searches Exa and fetches full content for the top results in one call.

Why

Agents currently need to call web_search_exa, parse URLs, then call web_fetch_exa. This adds latency and token overhead. The new tool performs both phases server-side and returns one structured markdown response.

Changes

• Added web_search_fetch_exa
• Registered it as a default tool
• Added search + batch /contents orchestration
• Added fetchNumResults clamping and search-only mode
• Added partial crawl error reporting
• Updated docs and discovery surfaces
• Added focused unit tests

Testing

• npm run typecheck
• npm run test
• Manual MCP Inspector validation:
  • happy path with numResults: 5, fetchNumResults: 3
  • clamp behavior with fetchNumResults: 99
  • search-only mode with fetchNumResults: 0
  • no-results branch