First step toward unifying all app modals on the Manage-Portfolio visual style.
Add, as shared material:: helpers (additive — no caller yet, no visible change):
- blur-overlay open refcount + 1-frame latch (Push/Pop/AnyBlurOverlayActive[LastFrame],
LatchBlurOverlayActive) so App::render's effect guard can be modal-agnostic;
- capture-frame query (IsCapturingBlurBackdrop) for scroll-fade suppression;
- RightAlignX and SegmentedControl (promoted verbatim from market_tab);
- BeginFadeScrollChild/EndFadeScrollChild in a dedicated overlay_scroll.h (kept
out of the widely-included draw_helpers.h because effects::ScrollFadeShader's GL
headers clash with SDL's in some TUs).
Also fix IsCurrentWindowOverlayDialog to prefix-match "##OverlayScrim" so suffixed
overlay windows are recognized by the modal-aware hover check.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
