feat: add Tavily Extract as alternative web content reader in visit_web

[tavily-integrations]

Summary

Adds Tavily Extract as a configurable alternative to Jina for URL content extraction in visit_web.py, controlled by the VISIT_PROVIDER environment variable. This is an additive change — existing Jina functionality is fully preserved and remains the default.

When VISIT_PROVIDER=tavily, content is fetched via TavilyClient.extract() and then fed into the same EXTRACTOR_PROMPT + LLM summarization pipeline used by the Jina path, ensuring consistent downstream behavior.

Changes

tools/tool/visit_web.py

• Imported TavilyClient from tavily
• Added VISIT_PROVIDER env var lookup (default: jina)
• Lazily initialize _tavily_client only when provider is tavily
• Added tavily_readpage(url) — fetches raw content via Tavily Extract API
• Added readpage_tavily(url, goal) — feeds Tavily content through the existing LLM summarization pipeline
• Added readpage(url, goal) — dispatcher that routes to Tavily or Jina based on VISIT_PROVIDER
• Updated visit_web() to use the readpage() dispatcher instead of calling readpage_jina() directly

config/.env

• Added VISIT_PROVIDER=jina (default placeholder)
• Added TAVILY_API_KEY= placeholder

requirements.txt

• Added tavily-python

Notes for reviewers

• The Tavily client is only initialized when VISIT_PROVIDER=tavily, so no API key is required for the default Jina path
• The summarization pipeline (EXTRACTOR_PROMPT → LLM → JSON parse) is identical between both paths
• All existing Jina code, retry loops, and env vars are untouched

Automated Review

• Passed after 1 attempt(s)
• Final review: The jina-to-tavily-extract migration is correct and complete. It adds Tavily Extract as a configurable alternative to Jina via the VISIT_PROVIDER env var, preserves all existing Jina logic, wires the dispatcher into visit_web(), and updates requirements.txt and config/.env. The Tavily SDK usage (TavilyClient.extract()) is correct. Several minor issues are noted — primarily code duplication, a potential conflict with the prerequisite unit's additions to requirements.txt and config/.env, and a null-safety gap in tavily_readpage() — but none are blocking.