feat(ui): add hover overlay scroll for left panel

FlatDropDown.pas

@@ -18,7 +18,7 @@ unit FlatDropDown;
 interface
 
 uses
-  Classes, SysUtils, Controls, Graphics, ExtCtrls, FlatButton;
+  Classes, SysUtils, Controls, Graphics, ExtCtrls, Math, FlatButton;
 
 type
   TButtonStyleProc     = procedure(B: TFlatButton; Active: Boolean) of object;
@@ -33,13 +33,14 @@ type
     FItemIndex:   Integer;
     FColumns:     Integer;
     FItemBtnH:    Integer;
+    FRightInset96: Integer;
     FIsOpen:      Boolean;
     FOnSelect:    TDropDownSelectEvent;
     procedure ItemClick(Sender: TObject);
     procedure PositionPopup;
   public
     constructor Create(AAnchor: TFlatButton; APopupParent: TWinControl;
-                       ACols, ABtnH: Integer);
+                       ACols, ABtnH: Integer; ARightInset96: Integer = 0);
     destructor Destroy; override;
     procedure SetItems(const ANames: array of string);
     procedure SetItemIndex(Idx: Integer);
@@ -54,13 +55,15 @@ type
 implementation
 
 constructor TFlatDropDown.Create(AAnchor: TFlatButton; APopupParent: TWinControl;
-                                  ACols, ABtnH: Integer);
+                                  ACols, ABtnH: Integer;
+                                  ARightInset96: Integer = 0);
 begin
   inherited Create;
   FAnchor      := AAnchor;
   FPopupParent := APopupParent;
   FColumns     := ACols;
   FItemBtnH    := ABtnH;
+  FRightInset96 := Max(0, ARightInset96);
   FItemIndex   := 0;
   FIsOpen      := False;
   FPopup := TPanel.Create(nil);
@@ -85,7 +88,11 @@ begin
     FPopup.Controls[0].Free;
   Count := Length(ANames);
   SetLength(FItemBtns, Count);
-  PopW := FPopupParent.ClientWidth;
+  // Popup может жить в контейнере с постоянно зарезервированным overlay-
+  // scrollbar gutter. Inset задаётся в 96-DPI координатах и пересчитывается
+  // при каждом наполнении: SetItems бывает и до, и после DPI-scale формы.
+  PopW := Max(1, FPopupParent.ClientWidth -
+                 FPopupParent.Scale96ToForm(FRightInset96));
   BtnW := (PopW - 4) div FColumns;
   FPopup.SetBounds(0, 0, PopW,
                    ((Count + FColumns - 1) div FColumns) * FItemBtnH);