localStorage key holding the active org brand overlay id, mirrored so the
inline pre-paint script can restore data-theme-overlay on first paint (the org
brand persists across the user's light/dark choice AND across logout). The overlay
CSS itself is a session-scoped Blob re-emitted at login bootstrap; the CSS text is
persisted beside it under PRELOAD_OVERLAY_CSS_KEY so
ThemeService.RestorePersistedBrandOverlay can put it back before first paint.
localStorage key holding the active org brand overlay id, mirrored so the inline pre-paint script can restore
data-theme-overlayon first paint (the org brand persists across the user's light/dark choice AND across logout). The overlay CSS itself is a session-scoped Blob re-emitted at login bootstrap; the CSS text is persisted beside it under PRELOAD_OVERLAY_CSS_KEY so ThemeService.RestorePersistedBrandOverlay can put it back before first paint.