fix: 统一所有弹框组件 padding + 主题风格

- ModalOverlay: 内容容器加 p-6 + border + shadow-xl
- alert-dialog: 统一主题变量 bg-[var(--dg-bg-secondary)] + rounded-xl
- sheet: SheetContent 加 p-6，移除 Header/Footer 重复 p-4
- drawer: DrawerContent 加 p-6，移除 Header/Footer 重复 p-4
- 所有弹框统一: p-6 padding + dg-border + shadow-xl + z-[101]

frontend/src/components/ui/alert-dialog.tsx

@@ -52,7 +52,7 @@ function AlertDialogContent({
       <AlertDialogPrimitive.Content
         data-slot="alert-dialog-content"
         className={cn(
-          "bg-background data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 fixed top-[50%] left-[50%] z-50 grid w-full max-w-[calc(100%-2rem)] translate-x-[-50%] translate-y-[-50%] gap-4 rounded-lg border p-6 shadow-lg duration-200 sm:max-w-lg",
+          "bg-[var(--dg-bg-secondary)] text-[var(--dg-text-primary)] border border-[var(--dg-border)] data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 fixed top-[50%] left-[50%] z-[101] grid w-full max-w-[calc(100%-2rem)] -translate-x-1/2 -translate-y-1/2 gap-4 rounded-xl p-6 shadow-xl duration-200 sm:max-w-lg",
           className
         )}
         {...props}

frontend/src/components/ui/drawer.tsx

@@ -56,7 +56,7 @@ function DrawerContent({
       <DrawerPrimitive.Content
         data-slot="drawer-content"
         className={cn(
-          "group/drawer-content bg-background fixed z-50 flex h-auto flex-col",
+          "group/drawer-content bg-[var(--dg-bg-secondary)] text-[var(--dg-text-primary)] border-[var(--dg-border)] fixed z-50 flex h-auto flex-col p-6",
           "data-[vaul-drawer-direction=top]:inset-x-0 data-[vaul-drawer-direction=top]:top-0 data-[vaul-drawer-direction=top]:mb-24 data-[vaul-drawer-direction=top]:max-h-[80vh] data-[vaul-drawer-direction=top]:rounded-b-lg data-[vaul-drawer-direction=top]:border-b",
           "data-[vaul-drawer-direction=bottom]:inset-x-0 data-[vaul-drawer-direction=bottom]:bottom-0 data-[vaul-drawer-direction=bottom]:mt-24 data-[vaul-drawer-direction=bottom]:max-h-[80vh] data-[vaul-drawer-direction=bottom]:rounded-t-lg data-[vaul-drawer-direction=bottom]:border-t",
           "data-[vaul-drawer-direction=right]:inset-y-0 data-[vaul-drawer-direction=right]:right-0 data-[vaul-drawer-direction=right]:w-3/4 data-[vaul-drawer-direction=right]:border-l data-[vaul-drawer-direction=right]:sm:max-w-sm",
@@ -77,7 +77,7 @@ function DrawerHeader({ className, ...props }: React.ComponentProps<"div">) {
     <div
       data-slot="drawer-header"
       className={cn(
-        "flex flex-col gap-0.5 p-4 group-data-[vaul-drawer-direction=bottom]/drawer-content:text-center group-data-[vaul-drawer-direction=top]/drawer-content:text-center md:gap-1.5 md:text-left",
+        "flex flex-col gap-0.5 group-data-[vaul-drawer-direction=bottom]/drawer-content:text-center group-data-[vaul-drawer-direction=top]/drawer-content:text-center md:gap-1.5 md:text-left",
         className
       )}
       {...props}
@@ -89,7 +89,7 @@ function DrawerFooter({ className, ...props }: React.ComponentProps<"div">) {
   return (
     <div
       data-slot="drawer-footer"
-      className={cn("mt-auto flex flex-col gap-2 p-4", className)}
+      className={cn("mt-auto flex flex-col gap-2", className)}
       {...props}
     />
   )

frontend/src/components/ui/sheet.tsx

@@ -56,7 +56,7 @@ function SheetContent({
       <SheetPrimitive.Content
         data-slot="sheet-content"
         className={cn(
-          "bg-background data-[state=open]:animate-in data-[state=closed]:animate-out fixed z-50 flex flex-col gap-4 shadow-lg transition ease-in-out data-[state=closed]:duration-300 data-[state=open]:duration-500",
+          "bg-[var(--dg-bg-secondary)] text-[var(--dg-text-primary)] border-[var(--dg-border)] data-[state=open]:animate-in data-[state=closed]:animate-out fixed z-50 flex flex-col gap-4 p-6 shadow-xl transition ease-in-out data-[state=closed]:duration-300 data-[state=open]:duration-500",
           side === "right" &&
             "data-[state=closed]:slide-out-to-right data-[state=open]:slide-in-from-right inset-y-0 right-0 h-full w-3/4 border-l sm:max-w-sm",
           side === "left" &&
@@ -83,7 +83,7 @@ function SheetHeader({ className, ...props }: React.ComponentProps<"div">) {
   return (
     <div
       data-slot="sheet-header"
-      className={cn("flex flex-col gap-1.5 p-4", className)}
+      className={cn("flex flex-col gap-1.5", className)}
       {...props}
     />
   )
@@ -93,7 +93,7 @@ function SheetFooter({ className, ...props }: React.ComponentProps<"div">) {
   return (
     <div
       data-slot="sheet-footer"
-      className={cn("mt-auto flex flex-col gap-2 p-4", className)}
+      className={cn("mt-auto flex flex-col gap-2", className)}
       {...props}
     />
   )