docs: add start_url parameter to browser and pool docs

[yummybomb]

Summary

Documents start_url for browser sessions and browser pools

• Adds SDK examples for browser creation with start_url
• Adds pool create and update examples with start_url
• Clarifies start_url navigation is best-effort and applies to newly created pool browsers
• Documents Chrome policy precedence and reused browser behavior
• Updates CLI docs for --start-url on browser create and pool create/update
• Adds --clear-start-url for clearing the pool start URL

Test plan

• git diff --check
• mintlify dev not run because the Mintlify CLI is not installed locally

[mintlify]

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Project	Status	Preview	Updated (UTC)
Kernel	🟢 Ready	View Preview	May 13, 2026, 6:49 PM

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[cursor]

Risk assessment: Very Low.

The current diff only adds start_url documentation and CLI reference text across existing MDX docs pages. There are no runtime code, docs config/navigation, generated API spec, schema, prompt, auth, permissions, or infrastructure changes, so the blast radius is limited to documentation rendering.

A prior approval is already present on the PR, and this synchronized update does not increase the risk level, so I’m not adding another approval.

  

_{Sent by Cursor Automation: Assign PR reviewers}

[cursor]

Risk assessment: Very Low.

The synchronized diff only adds start_url documentation and CLI flag descriptions in existing MDX docs pages (browsers/create-a-browser.mdx, browser pool docs, and CLI reference). There are no runtime code, config/navigation, schema, prompt-instruction, auth/permissions, or infrastructure changes, so the blast radius is limited to documentation rendering.

The PR is already approved, and this update does not increase the risk level, so I’m not adding another approval or dismissing the existing one.

  

_{Sent by Cursor Automation: Assign PR reviewers}