Fix browser probe navigation timeout

[chubes4]

Summary

• Pass the caller-declared wordpress.browser-probe timeout= budget into Playwright navigation.
• Apply the same timeout to selector waits so slow-but-valid pages are governed by the probe budget.
• Add a focused smoke proving a 180s timeout reaches navigation and selector waits.

Fixes #939.

Verification

• npm run browser-probe-navigation-timeout-smoke
• npm run build

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Implemented the timeout propagation fix, added focused smoke coverage, and ran verification commands for Chris to review.