feat: add Tavily as priority search provider with DDG/Google fallback

[tavily-integrations]

Summary

• Added Tavily as a configurable, priority search provider for web search queries
• When TAVILY_API_KEY is set, Tavily is used as the primary search backend
• Existing Google Custom Search and DuckDuckGo providers are preserved as fallback when Tavily is not configured or returns no results
• This is an additive change — no existing functionality is removed or altered

Files changed

• pyproject.toml — Added tavily-python>=0.5.0 to project dependencies
• .env.example — Added TAVILY_API_KEY env var with documentation comment
• aient/aient/plugins/websearch.py — Added gettavilysearchurl() function using TavilyClient SDK; modified get_search_url() to prefer Tavily when the API key is present, falling back to Google/DDG otherwise
• config.py — Added TAVILY_API_KEY environment variable read

Dependency changes

• Added tavily-python>=0.5.0 to pyproject.toml

Environment variable changes

• Added TAVILY_API_KEY (optional) — when set, Tavily is used as the primary search provider

Notes for reviewers

• The gettavilysearchurl() function follows the same error-handling and return pattern as getddgsearchurl() and getgooglesearchurl()
• Tavily import is done lazily inside the function to avoid import errors when the package is not installed
• The fallback logic ensures zero disruption to existing deployments without TAVILY_API_KEY

🤖 Generated with Claude Code

Automated Review

• Passed after 3 attempt(s)
• Final review: The migration correctly adds Tavily as a configurable, primary search provider with Google/DuckDuckGo as fallback. All required files are updated: pyproject.toml has the dependency, uv.lock resolves tavily-python v0.7.23 with its transitive dependencies (tiktoken, regex), .env.example and README.md document TAVILY_API_KEY, and the aient submodule contains proper integration code using TavilyClient. The implementation is additive and backward-compatible — existing behavior is fully preserved when TAVILY_API_KEY is not set.