feat(modals): stronger backdrop blur + dim, and anchor floating modals on light skins

The modal audit found card-less (floating) dialogs read slightly unanchored on
the light skins: the blur backdrop's dim is a theme-tinted frost, which darkens
on dark themes (content pops) but WHITENS on light themes — so sparse content
floated in a near-white expanse with no figure/ground separation.

- Light themes now get a neutral dark veil instead of the whitening frost, which
  darkens the surround and makes the modal's fields/buttons stand out.
- Dark themes keep the theme-tinted frost, a touch stronger (alpha 70 -> 90).
- Full-window blur deepened (64 -> 96) so the backdrop reads clearly frosted.

Verified on the headless sweep across light + dark: backup / debug-gate now
read as anchored groups; content-heavy modals (daemon-update, settings, wallets)
are unaffected (their own surfaces stand out), and dark-skin text contrast
improves for free from the deeper dim.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/material/draw_helpers.h

@@ -729,10 +729,18 @@ inline void DrawFullWindowBlurBackdrop(ImDrawList* dl, const ImVec2& pMin, const
         // panel skips acrylic (IsFullWindowBlurOverlayActive), so the backdrop is the SOLE applyBlur
         // caller — no other radius contends for the shared, radius-keyed blur cache.
         auto params = GetCurrentAcrylicTheme().card;
-        params.blurRadius = 64.0f;                            // strong full-window blur
+        params.blurRadius = 96.0f;                            // strong full-window blur (deeper than panels)
         params.fallbackColor.w = 1.0f;                        // full-strength blur so the live content reads
         effects::ImGuiAcrylic::DrawAcrylicRect(dl, pMin, pMax, params, 0.0f);
-        dl->AddRectFilled(pMin, pMax, WithAlpha(Background(), 70));  // subtle theme-tinted frost so the card reads as foreground
+        // Dim over the blur so the floating (card-less) modal reads as foreground. On DARK themes the
+        // theme-tinted frost darkens the backdrop and the light content pops. On LIGHT themes that same
+        // tint whitens the backdrop and leaves card-less content with no figure/ground separation — so
+        // light themes get a neutral dark veil instead, which also makes the modal's fields/buttons stand
+        // out from the (now slightly greyed) surround. Both a touch stronger than before (was alpha 70).
+        if (IsLightTheme())
+            dl->AddRectFilled(pMin, pMax, IM_COL32(16, 18, 24, 56));     // neutral dark veil anchors on white
+        else
+            dl->AddRectFilled(pMin, pMax, WithAlpha(Background(), 90));  // theme-tinted darken, stronger
     }
 }