fix: reject JSON arrays as 3p and WebMCP tool params

[kevin9327]

Summary

execute_3p_developer_tool and execute_webmcp_tool parse a JSON string as params. Arrays pass typeof parsed === 'object' && parsed !== null, so [] skipped the object check and failed later with a misleading error (Tool not found or a Puppeteer private-field TypeError).

Reject arrays the same way wsHeaders already does.

Testing

• npm run test tests/tools/thirdPartyDeveloper.test.ts tests/tools/webmcp.test.ts
• npm run typecheck
• npm run check-format

AI-assisted (Grok)

[google-cla]

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[wolfib]

The change looks good to me, thanks!
Please sign the CLA and we can get this merged.

[kevin9327]

I have signed the Google Individual CLA now (GitHub username kevin9327). The cla/google check on this PR and on #2781, #2782, #2783 and #2784 still shows the result from before I signed, and I can't re-run it from my side. Could you re-run it when you get a chance? Thanks.

[wolfib]

Thanks! LGTM