feat: add set_extra_http_headers tool for Network.setExtraHTTPHeaders

[pedrodurek]

Summary

Add a new set_extra_http_headers tool that calls Puppeteer's page.setExtraHTTPHeaders() (which uses CDP Network.setExtraHTTPHeaders under the hood).

Closes #1175

Tool Definition

• Name: set_extra_http_headers
• Category: Network (alongside list_network_requests and get_network_request)
• Schema: headers — a Record<string, string> of header name-value pairs
• Behavior:
  • Headers apply to all subsequent requests on the selected page (document, scripts, fetch, XHR, images, etc.)
  • Headers persist across navigations until explicitly cleared with {}
  • Returns a confirmation message listing the header names set, or "cleared" when empty

Use Case

This enables setting custom HTTP headers on all requests — including the initial document navigation and <script> tag loads — which initScript cannot do since it runs after the document is already fetched.

Changes

• src/tools/network.ts — Added setExtraHTTPHeaders page tool using definePageTool
• tests/tools/network.test.ts — Added 3 test cases:
  1. Verifies headers arrive at the server
  2. Verifies clearing headers with {}
  3. Verifies headers persist across navigations

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[OrKoN]

Thanks for the PR! I think we should align with the suggestion in this comment #1175 (comment) and add this to the emulation tool.