feat: add Tavily as configurable search provider alongside SearXNG

[tavily-integrations]

Summary

• Added Tavily as an alternative search backend in SearchWeb, selectable via SEARCH_PROVIDER env var
• SearXNG remains the default provider; all existing SearXNG infrastructure is unchanged
• Tavily results are normalized to match SearXNG result format (link, title, snippet keys) for seamless downstream compatibility

Files changed

• requirements.txt — Added tavily-python dependency
• model_config.py — Added SEARCH_PROVIDER (default 'searxng') and TAVILY_API_KEY config vars
• utils/websearch_utils.py — Extended SearchWeb class with Tavily client init and _tavily_search() method; query_search() routes based on provider
• .env — Documented SEARCH_PROVIDER and TAVILY_API_KEY as optional commented-out vars
• docker-compose.yml — Added SEARCH_PROVIDER and TAVILY_API_KEY as optional env entries on the app service

Dependency changes

• Added tavily-python to requirements.txt

Environment variable changes

• SEARCH_PROVIDER — optional, defaults to searxng; set to tavily to use Tavily
• TAVILY_API_KEY — required only when SEARCH_PROVIDER=tavily

Notes for reviewers

• This is an additive change; no existing SearXNG behavior is modified
• The Tavily search uses search_depth="basic" (1 credit per query) for cost efficiency
• Result normalization ensures all downstream code that consumes search results continues to work unchanged

Automated Review

• Passed after 1 attempt(s)
• Final review: The Tavily migration is correct, additive, and well-scoped. The implementation properly routes between SearXNG and Tavily based on SEARCH_PROVIDER, normalizes Tavily results to match the existing dict format (link/title/snippet), and covers all required files. No regressions to existing SearXNG functionality. Three minor issues noted but none are blockers.