feat: add Tavily as opt-in parallel web search provider

[tavily-integrations]

Summary

Adds Tavily as a configurable alternative web search provider alongside the existing Brave Search integration. This is an additive migration — Brave Search remains fully functional and is the default; Tavily is opt-in for users who configure TAVILY_API_KEY.

Changes

Dependencies

• Added tavily-mcp (^0.1.4) to package.json

MCP Configuration

• Added tavily-search stdio MCP server entry in mcp.example.json with TAVILY_API_KEY env var
• Existing brave-search entry is unchanged

Documentation (README.md)

• Updated MCP integration count from 5 to 6
• Added Tavily row to MCP Servers table
• Added Tavily to the architecture MCP layer diagram
• Added TAVILY_API_KEY env var documentation section

Skills

• skills/web-search/SKILL.md — Added provider-selection clause: prefer tavily_search if the Tavily MCP server is active, else use brave_web_search
• skills/broad-web-search/SKILL.md — Same provider-selection clause, updated hard constraints to reference both providers' parameter names

Files Changed

• package.json
• mcp.example.json
• README.md
• skills/web-search/SKILL.md
• skills/broad-web-search/SKILL.md

Environment Variable Changes

• Added TAVILY_API_KEY — Tavily API key (opt-in, get free key at https://app.tavily.com)
• Existing BRAVE_API_KEY is unchanged

Notes for Reviewers

• ~45 additional skill files reference brave_web_search directly. These are intentionally left unchanged under the additive strategy — they continue to work with Brave Search. The two canonical web-search SOPs now handle provider selection, which covers the primary entry points.
• JSON validity of package.json and mcp.example.json verified.

Automated Review

• Passed after 1 attempt(s)
• Final review: The migration correctly adds Tavily as an opt-in parallel web search provider alongside Brave Search. All five reported files are modified appropriately: package.json gains the tavily-mcp dependency, mcp.example.json gains a well-formed server config block, README.md updates counts and documentation, and both skill files gain provider-selection clauses with proper fallback logic. The implementation is purely additive — Brave Search is fully preserved. One minor inconsistency: the frontmatter description field of broad-web-search/SKILL.md still hard-references brave_web_search count=10 while the body now supports both providers.