chore: remove About link from header and language switcher from about pages (#464)

- Remove About link and sponsor notice icon from chat panel header
- Remove language switcher (English | 中文 | 日本語) from all about pages
- Fix About link in settings dialog to use current language
- Remove unused sponsorTooltip translation key from all dictionaries

components/chat-panel.tsx

@@ -3,14 +3,12 @@
 import { useChat } from "@ai-sdk/react"
 import { DefaultChatTransport } from "ai"
 import {
-    AlertTriangle,
     MessageSquarePlus,
     PanelRightClose,
     PanelRightOpen,
     Settings,
 } from "lucide-react"
 import Image from "next/image"
-import Link from "next/link"
 import type React from "react"
 import { useCallback, useEffect, useRef, useState } from "react"
 import { flushSync } from "react-dom"
@@ -952,32 +950,6 @@ export default function ChatPanel({
                                 Next AI Drawio
                             </h1>
                         </div>
-                        {!isMobile && (
-                            <Link
-                                href="/about"
-                                target="_blank"
-                                rel="noopener noreferrer"
-                                className="text-sm text-muted-foreground hover:text-foreground transition-colors ml-2"
-                            >
-                                {dict.nav.about}
-                            </Link>
-                        )}
-                        {!isMobile && (
-                            <Link
-                                href="/about"
-                                target="_blank"
-                                rel="noopener noreferrer"
-                            >
-                                <ButtonWithTooltip
-                                    tooltipContent={dict.nav.sponsorTooltip}
-                                    variant="ghost"
-                                    size="icon"
-                                    className="h-6 w-6 text-amber-500 hover:text-amber-600"
-                                >
-                                    <AlertTriangle className="h-4 w-4" />
-                                </ButtonWithTooltip>
-                            </Link>
-                        )}
                     </div>
                     <div className="flex items-center gap-1 justify-end overflow-visible">
                         <ButtonWithTooltip