🎨 style: remove overly vibrant colors and simplify UI design

- Remove colorful gradient backgrounds from dashboard panel headers in Detail page
- Replace custom header styling with default Semi-UI card title styling
- Remove background images and gradient overlays from all authentication pages
- Simplify authentication page layouts with clean gray backgrounds
- Update title text colors from white to dark gray for better contrast
- Remove unnecessary z-index layering and complex positioning
- Clean up unused background image imports

This change creates a more professional and consistent visual appearance
across the application by removing distracting visual elements.

web/src/components/auth/RegisterForm.js

@@ -33,7 +33,6 @@ import WeChatIcon from '../common/logo/WeChatIcon.js';
 import TelegramLoginButton from 'react-telegram-login/src';
 import { UserContext } from '../../context/User/index.js';
 import { useTranslation } from 'react-i18next';
-import Background from '/example.png';
 
 const RegisterForm = () => {
   const { t } = useTranslation();
@@ -272,7 +271,7 @@ const RegisterForm = () => {
         <div className="w-full max-w-md">
           <div className="flex items-center justify-center mb-6 gap-2">
             <img src={logo} alt="Logo" className="h-10 rounded-full" />
-            <Title heading={3} className='!text-white'>{systemName}</Title>
+            <Title heading={3} className='!text-gray-800'>{systemName}</Title>
           </div>
 
           <Card className="shadow-xl border-0 !rounded-2xl overflow-hidden">
@@ -379,7 +378,7 @@ const RegisterForm = () => {
         <div className="w-full max-w-md">
           <div className="flex items-center justify-center mb-6 gap-2">
             <img src={logo} alt="Logo" className="h-10 rounded-full" />
-            <Title heading={3} className='!text-white'>{systemName}</Title>
+            <Title heading={3} className='!text-gray-800'>{systemName}</Title>
           </div>
 
           <Card className="shadow-xl border-0 !rounded-2xl overflow-hidden">
@@ -542,17 +541,8 @@ const RegisterForm = () => {
   };
 
   return (
-    <div className="min-h-screen relative flex items-center justify-center py-12 px-4 sm:px-6 lg:px-8 overflow-hidden">
-      <div
-        className="absolute inset-0 z-0 bg-cover bg-center scale-125 opacity-100"
-        style={{
-          backgroundImage: `url(${Background})`
-        }}
-      ></div>
-
-      <div className="absolute inset-0 bg-gradient-to-br from-teal-500/30 via-blue-500/30 to-purple-500/30 backdrop-blur-sm z-0"></div>
-
-      <div className="w-full max-w-sm relative z-10">
+    <div className="bg-gray-100 flex items-center justify-center py-12 px-4 sm:px-6 lg:px-8">
+      <div className="w-full max-w-sm">
         {showEmailRegister || !(status.github_oauth || status.oidc_enabled || status.wechat_login || status.linuxdo_oauth || status.telegram_oauth)
           ? renderEmailRegisterForm()
           : renderOAuthOptions()}