02ffdaba68d418dd449d613c96e76cd57f7e3c9a  Source element moving steps doesn't handle media and model elements

Classified as not security-relevant.
Triage note: HTMLSourceElement::movingSteps now computes newParent once and calls sourceWasAdded()/sourcesChanged() on HTMLMediaElement/HTMLModelElement; a state-sync correctness change with no memory-safety or origin bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), area:Source/WebCore/html (+2.0), surgical (+1.3)