1392437bb060048807e94d171c0fdf45e7d27301  [Site Isolation] Deliver a received remote-control command to the same session with and without site isolation

Classified as not security-relevant.
Triage note: Adds a targetSession parameter so a cross-process-elected NowPlaying owner receives remote commands, plus GPU-process test plumbing in Internals. Media-session feature/refactor with no security 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), null_guard (+2.59), msg_soft (+1.0), large_churn (-2.0)