fix: drag-to-transfer drop not triggering transfer dialog

s_dropTargetIdx was reset to -1 unconditionally each frame, including
the release frame. Since drop target detection runs in PASS 2 (after
the drop handler), the target was always -1 when checked. Only reset
while mouse button is held so the previous frame's value is preserved.

Also bump version to 1.2.0-rc1 and add release notes.

src/ui/windows/balance_tab.cpp

@@ -1557,8 +1557,9 @@ static void RenderSharedAddressList(App* app, float listH, float availW,
         bool mouseDown = ImGui::IsMouseDown(ImGuiMouseButton_Left);
         bool mouseClicked = ImGui::IsMouseClicked(ImGuiMouseButton_Left);
 
-        // Reset drop target each frame — it gets set only if mouse is over a row
-        if (s_dragActive) s_dropTargetIdx = -1;
+        // Reset drop target each frame — it gets set only if mouse is over a row.
+        // Preserve the drop target on the release frame so the drop handler can use it.
+        if (s_dragActive && mouseDown) s_dropTargetIdx = -1;
 
         if (s_dragIdx >= 0 && !mouseDown) {
             // Mouse released — copy if it was a click (no drag activated)