fix(browser): bound capture work and preserve observation gaps
Own service-worker CDP registrations and retry failed teardown. Admit redaction and network metadata against remaining capture capacity, retain explicit omission reasons, and preserve source URL, redirect ancestry, caller-selected content, and historical capture values. Forward CLI cancellation through provider cleanup.
Reviewed fixes: #2263, #2637, #2767, #2845, #2859, #2863, #2872, #2874, #2876, #2879, #2955, #2957, #2961, #3033.
Validation: 25 current event/network source tests passed; earlier focused browser lanes passed 201 source tests and 176 boundary tests with two skips, plus 35 Python tests. Real browser/Windows lanes were not rerun. Playwright allocation before admission remains unbounded by these retention limits.
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