36c8ec5fdabfade0a60bd8adb3623ee023ae5eff  Make InspectorOverlay frame-relative so it can draw in a subframe process

Classified as not security-relevant.
Triage note: Introduces InspectorOverlayOwner and frame-scoped overlays, replaces page()->mainFrame() assumptions with frameForGeometry() and adds many null-view guards (if (!containingView) return); inspector/devtools-only, not reachable by web content.
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), large_churn (-2.0)