Add start URL flags to browser commands

[yummybomb]

Summary

• update the Go SDK to v0.53.0 for start_url fields
• add --start-url to browser create and browser pool create/update
• add --clear-start-url for browser pool update
• reject --start-url values that are parsed from another flag token
• show Start URL in browser and pool outputs
• document the new flags

Test plan

• go test ./cmd
• make test
• make build
• KERNEL_API_KEY=test ./bin/kernel browser-pools update pool123 --start-url --discard-all-idle returns --start-url requires a URL value
• KERNEL_API_KEY=test ./bin/kernel browsers create --start-url --headless returns --start-url requires a URL value
• ./bin/kernel browser-pools update --help
• ./bin/kernel browser-pools update pool123 --start-url https://example.com --clear-start-url returns cannot specify both --start-url and --clear-start-url

---

Note

Low Risk
Low risk CLI enhancement that adds optional flags and output fields; main risk is minor behavior changes in flag validation and pool update semantics.

Overview
Adds --start-url support to kernel browsers create and kernel browser-pools create/update, wiring it through to the SDK request params and displaying the configured/returned Start URL in human-readable outputs.

Introduces --clear-start-url for pool updates (mutually exclusive with --start-url) and rejects --start-url values that look like another flag token (e.g. --headless) to prevent accidental mis-parsing.

Bumps kernel-go-sdk to v0.53.0, adds tests covering the new start URL behavior, and updates README flag documentation.

^{Reviewed by Cursor Bugbot for commit 068a880. Bugbot is set up for automated code reviews on this repo. Configure here.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	golang/​github.com/​kernel/​kernel-go-sdk@​v0.52.0 ⏵ v0.53.0	+1

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[firetiger-agent]

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