fix(dialtesting): upstream Lightpanda 0.4 screenshot integration

[NaR82n]

Upstream the Lightpanda 0.4.0-g1 integration currently carried by DataKit MR !4157 as vendor patches. Enable optional PNG screenshots and viewport settings, use the updated resource/CIDR arguments, bound screenshot capture and clean discarded retry images. Avoid creating an uncancelled intermediate context for deadline-bearing actions.

Validation: go test -race ./dialtesting/browserdial/... passed. Existing argument tests were updated for the new CLI. Real Lightpanda binary compatibility was not exercised. Repository-wide lint reported 67 issues outside these changed files; copyright check reported existing missing headers (headers added to the migrated files). Full make test is time-bounded and not a release gate proven by this PR.

Requires Lightpanda 0.4.0-g1; retains the parameter adaptation already shipped in the DataKit change.

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