perf(overview): clip the address list to the visible rows

The Overview address list built all N rows on every frame (icons,
labels, balances, buttons, an InvisibleButton and a context-menu
check per address) and allocated a vector of N row positions, however
few rows fit on screen; the edge mask then walked all their vertices.

An ImGuiListClipper now submits only the rows that intersect the
list's clip rect, plus:
- one guard row on each side, so dividers and anti-aliased edges at
  the clip boundary are drawn as before;
- the row being dragged and the row whose context menu is open, so
  drag-to-reorder and the menu keep working when they scroll away;
- the rows keyboard navigation targets (kept by the clipper itself).

Before each row the cursor is put back exactly where the unclipped
loop left it, so the density-scaled spacing, which depends on the
cursor position, and every row's geometry are unchanged. Row tops are
computed from the index, so the per-frame vector is gone, and the
scroll extent is the same. The row model (sort, filter) is still
rebuilt over all addresses each frame.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/windows/balance_address_list.cpp

@@ -2,6 +2,7 @@
 
 #include <algorithm>
 #include <cctype>
+#include <cmath>
 #include <cstdio>
 
 namespace dragonx {
@@ -106,5 +107,26 @@ std::string FormatAddressUsdValue(double balance, double priceUsd)
     return buffer;
 }
 
+AddressRowWindow ComputeAddressRowWindow(float clipMinY, float clipMaxY, float startY, float rowH, int rowCount)
+{
+    AddressRowWindow w;
+    if (rowCount <= 0) return w;
+    w.end = rowCount;                                        // fail open (every row) on degenerate input
+    if (!(rowH > 0.0f)) return w;
+    const double first = std::floor(((double)clipMinY - startY) / rowH) - 1.0;
+    const double last  = std::ceil(((double)clipMaxY - startY) / rowH) + 1.0;   // exclusive
+    if (!std::isfinite(first) || !std::isfinite(last)) return w;
+    w.begin = (int)std::clamp(first, 0.0, (double)rowCount);
+    w.end   = (int)std::clamp(last, (double)w.begin, (double)rowCount);
+    return w;
+}
+
+float AddressRowEntryCursorY(int i, float startY, float rowH, float itemSpacingY)
+{
+    if (i <= 0) return startY;
+    const float prevTop = startY + (i - 1) * rowH;          // the row loop's row-top expression
+    return (float)(int)(prevTop + rowH + itemSpacingY);     // ImGui::ItemSize: IM_TRUNC(line_y1 + line_height + ItemSpacing.y)
+}
+
 } // namespace ui
 } // namespace dragonx