style(ui): refine header layout and AppSwitcher color scheme

Improve application header and component styling:

## App.tsx Header Layout
- Wrap title and settings button in flex container with gap
- Add vertical divider between title and settings icon
- Apply responsive padding (pl-1 sm:pl-2)
- Reformat JSX for better readability (prettier)
- Fix string template formatting in className

## AppSwitcher Color Update
- Change Claude tab gradient from orange/amber to teal/emerald/green
- Update shadow color to match new teal theme
- Change hover color from orange-500 to teal-500
- Align visual style with emerald/teal brand colors

## Dialog Component Cleanup
- Remove default close button (X icon) from DialogContent
- Allow parent components to control close button placement
- Remove unused lucide-react X import

## index.css Header Border
- Add top border (2px solid) to glass-header
- Apply to both light and dark mode variants
- Improve visual separation of header area

These changes enhance visual consistency and modernize the UI
appearance with a cohesive teal color scheme.

src/components/ui/dialog.tsx

@@ -1,6 +1,5 @@
 import * as React from "react";
 import * as DialogPrimitive from "@radix-ui/react-dialog";
-import { X } from "lucide-react";
 import { cn } from "@/lib/utils";
 
 const Dialog = DialogPrimitive.Root;
@@ -84,10 +83,6 @@ const DialogContent = React.forwardRef<
           {...props}
         >
           {children}
-          <DialogPrimitive.Close className="absolute right-4 top-4 rounded-sm opacity-70 ring-offset-background transition-opacity hover:opacity-100 focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2 disabled:pointer-events-none">
-            <X className="h-4 w-4" />
-            <span className="sr-only">关闭</span>
-          </DialogPrimitive.Close>
         </DialogPrimitive.Content>
       </DialogPortal>
     );