fix: treat timeout 0 as the default wait, not unlimited

[gyanu2507]

Summary

timeoutSchema documents that timeout: 0 uses the default wait. The transform used value && value <= 0, which is falsy for 0, so the number 0 was passed through to Puppeteer. In Puppeteer, timeout: 0 means wait forever.

Agents that pass 0 expecting the normal default can hang navigate_page / new_page on a stuck load.

Test plan

• timeout: 0 and -1 parse to undefined
• timeout: 500 stays 500
• omitted timeout stays omitted

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