feat: add Tavily as parallel search provider option

[ParakhJaggi]

Summary

Adds Tavily as a configurable search and content extraction provider alongside the existing Querit.ai integration. This is an additive change — all existing Querit code, dependencies, and env vars remain untouched.

What changed

Provider selection logic

• New selectProvider() helper in search.js reads SEARCH_PROVIDER env var ("tavily" or "querit")
• Falls back to auto-detection: if TAVILY_API_KEY is set and QUERIT_API_KEY is absent, uses Tavily; otherwise defaults to Querit

search.js

• Added tavilySearch() function using @tavily/core SDK
• Maps CLI flags to Tavily params: --site-include→includeDomains, --site-exclude→excludeDomains, --date→timeRange, --country→country, -n→maxResults (capped at 20)
• Prints warning when --lang is used with Tavily (unsupported)
• Normalizes Tavily results to match existing formatResults() shape
• Updated usage() to document both providers

content.js

• Added tavilyExtract() function using Tavily Extract API
• Added extractWithProvider() dispatcher: tries Tavily Extract when configured, falls back to existing jsdom+Readability pipeline on failure
• Existing extraction code completely unchanged

Documentation

• SKILL.md: Added TAVILY_API_KEY and SEARCH_PROVIDER as optional env vars in metadata
• README.md: Added Tavily configuration section, provider selection docs, and Tavily-specific notes (max results, unsupported filters)

Files changed

• package.json — added @tavily/core dependency
• package-lock.json — lockfile updated
• search.js — provider selection + Tavily search path
• content.js — Tavily Extract with jsdom fallback
• SKILL.md — optional env var documentation
• README.md — Tavily setup and provider selection docs

Dependency changes

• Added @tavily/core@^0.7.2 to package.json

Environment variable changes

• TAVILY_API_KEY — Tavily API key, required when using Tavily provider
• SEARCH_PROVIDER — optional, "tavily" or "querit"; auto-detects if unset

Notes for reviewers

• Tavily max results is 20 (vs Querit's 100); a warning is emitted if -n exceeds 20
• --lang filter has no Tavily equivalent; a warning is printed and the filter is ignored
• Tavily Extract failure gracefully falls back to the existing jsdom pipeline

Automated Review

• Passed after 2 attempt(s)
• Final review: The migration is well-implemented and all four issues from the previous review attempt are correctly addressed: SKILL.md requires.env is now empty with both keys moved to optionalEnv; content.js usage() documents TAVILY_API_KEY; extractWithProvider() warns when SEARCH_PROVIDER=tavily but TAVILY_API_KEY is missing; and SKILL.md limitations shows provider-specific max results. The Querit path is fully preserved as an else-branch, the auto-detection logic is consistent between search.js and content.js, dependencies are correctly updated in both package.json and package-lock.json, and README.md is updated with clear dual-provider setup instructions. Three minor issues remain but none are blocking.