[WIP] Implement web_search tool using Brave API

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement web_search tool (Brave API)</issue_title>
<issue_description>Priority: P1 (required for Rook autonomy)

Spec:

• Accept parameters: {query, count?} (default count: 5)
• Integrate Brave Search API (BRAVE_API_KEY env var)
• Return formatted results: title, URL, snippet
• Handle rate limits and errors gracefully

Files:

• Create src/tools/web-search.ts
• Register in tool registry
• Add JSON Schema definition
• Document env var requirement in README

Tests:

• Mock Brave API responses
• Integration test with agent loop
• Error handling (invalid key, rate limit)

Acceptance:

• Tool executes via agent loop
• Rook can research topics autonomously
• Proper error messages for API failures

Ref: gap-analysis-report.md P1-2</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement web_search tool (Brave API) #123

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