#3403 fix(extension): prune descendant frameOwnerPage entries on frame detach and page close

Summary

Closing pages with nested frames left stale frameOwnerPage entries: Page.frameDetached deleted only the detached frame id and did not prune descendants still mapped to the same owner.

This PR prunes the detached frame and every descendant still owned by the same page on detach (unless reason === \"swap\"), and applies the same prune on page close before clearing remaining entries for the closed page.

Fixes https://github.com/browserbase/stagehand/issues/3240

Test plan

• OOPIF context fixture failed on unmodified upstream main (NESTED_FRAME / same-origin grandchildren stayed in the map) and passes with this change
• Extension unit tests otherwise green (extension-build checks need a built dist/ not produced by this change)

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Summary by cubic

Fixes stale frameOwnerPage entries left behind when frames detach or pages close, so a reused browser context no longer retains ownership of closed pages.

• Prunes the detached frame and all descendants still owned by the same page on frame detach, unless the reason is swap.
• Applies the same prune on page close and keeps frames owned by other pages intact.