muxg: finish and gate recovery and force-End native popovers

open   by a73x

S2 is intentionally stopped before delivery. Controller/theme and generic renderer work exists on the experimental branch, but real-window lifecycle validation exposed retained-frame/glyph rendering after recovery reattach, and fixtures are incomplete/uncommitted.

Scope: resume from a reviewed design after the S1 shipment decision; make centered recovery and force-End popovers visible and reliable, preserve captured attachment identity, Cancel default/destructive confirmation, pending-End nonmodality, no click-through, focus-loss safety, glyph-atlas preparation before UV normalization, and overlay-last ordering. Keep legacy picker and empty-workspace popup paths unchanged.

Acceptance: deterministic real-window lifecycle coverage, native-core-test, native, native-e2e, focused lifecycle fixture, check, and independent review.

Do not ship the current stopped S2 experiment without re-review.