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.h

@@ -89,6 +89,19 @@ void InvalidateCapture();
  */
 ImDrawCallback GetBackgroundCaptureCallback();
 
+/**
+ * @brief Returns a draw callback that captures the LIVE framebuffer (no dirtyFrames_
+ * gate). Insert it at the START of a full-window modal overlay's draw list — before the
+ * overlay draws its own backdrop — so the acrylic blurs the live app UI behind the modal:
+ * @code
+ *   ImDrawList* dl = ImGui::GetWindowDrawList();
+ *   dl->AddCallback(ImGuiAcrylic::GetLiveCaptureCallback(), nullptr);
+ *   dl->AddCallback(ImDrawCallback_ResetRenderState, nullptr);
+ *   // ... then draw the overlay's acrylic/dim backdrop ...
+ * @endcode
+ */
+ImDrawCallback GetLiveCaptureCallback();
+
 // ============================================================================
 // Drawing Functions
 // ============================================================================