feat(effects): overlay-time live-framebuffer blur behind the portfolio modal

The acrylic system only blurred a frozen snapshot of the static app background. Add
an overlay-time re-capture so the Manage-portfolio modal blurs the LIVE tab content
behind it.

- AcrylicMaterial::captureLiveFramebuffer() (GL blit of FB 0 / DX11 CopyResource of the
  backbuffer + no-backend stub) mirrors captureBackgroundDirect but bypasses the
  dirtyFrames_ gate so it refreshes every frame the overlay is open, forcing a re-blur.
- ImGuiAcrylic::GetLiveCaptureCallback() returns a draw callback for it.
- market_tab: the modal inserts that callback (+ ImDrawCallback_ResetRenderState) at the
  START of its overlay draw list, before the backdrop, so the capture holds the app UI
  drawn below and the backdrop blurs it. On close, InvalidateCapture() re-captures the
  background so other glass panels don't keep blurring the stale live capture.
- Panel theme-effects are suppressed during the market render while the modal is open
  (their foreground-draw-list borders draw above all windows and would otherwise bleed
  over the overlay). Market tab body is rendered again (no longer skipped).
- Backdrop draws the acrylic at full strength (fallbackColor.w=1) over an opaque base so
  the blurred content reads clearly; lighter dim.

Design mapped via an Explore investigation of the capture/blur pipeline; compiles on
both OpenGL (Linux) and DX11 (Windows cross-build). Needs on-device visual verification.

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

src/ui/effects/imgui_acrylic.cpp

@@ -236,6 +236,17 @@ ImDrawCallback GetBackgroundCaptureCallback()
     return BackgroundCaptureCallback;
 }
 
+static void LiveCaptureCallback(const ImDrawList*, const ImDrawCmd*)
+{
+    if (!s_initialized) return;
+    getAcrylicMaterial().captureLiveFramebuffer();
+}
+
+ImDrawCallback GetLiveCaptureCallback()
+{
+    return LiveCaptureCallback;
+}
+
 // ============================================================================
 // Drawing Functions
 // ============================================================================
@@ -657,6 +668,7 @@ void BeginFrame(int, int) {}
 void CaptureBackground() {}
 void InvalidateCapture() {}
 ImDrawCallback GetBackgroundCaptureCallback() { return nullptr; }
+ImDrawCallback GetLiveCaptureCallback() { return nullptr; }
 
 void DrawAcrylicRect(ImDrawList* drawList, 
                      const ImVec2& pMin, const ImVec2& pMax,