feat(branding): 启用新版 SVG logo 并在 README 头部展示

- 新增 assets/logo.svg 作为项目默认 logo（512x512 深色圆角底 + 渐变 S 标）
- 前端 favicon 与组件兜底 logo 由 logo.png 切换为 frontend/public/logo.svg
- 三个 README（EN/CN/JA）头部新增居中 logo 与标题布局
- 删除旧 logo.png 及多余的 lobe 变体 SVG

frontend/src/components/layout/AppSidebar.vue

@@ -14,7 +14,7 @@
         class="sidebar-logo flex h-9 w-9 items-center justify-center overflow-hidden rounded-xl shadow-glow transition-opacity hover:opacity-80"
         @click="handleMenuItemClick(homePath)"
       >
-        <img v-if="settingsLoaded" :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
+        <img v-if="settingsLoaded" :src="siteLogo || '/logo.svg'" alt="Logo" class="h-full w-full object-contain" />
       </router-link>
       <div class="sidebar-brand" :class="{ 'sidebar-brand-collapsed': sidebarCollapsed }" :aria-hidden="sidebarCollapsed ? 'true' : 'false'">
         <router-link

frontend/src/components/layout/AuthLayout.vue

@@ -33,7 +33,7 @@
           <div
             class="mb-4 inline-flex h-16 w-16 items-center justify-center overflow-hidden rounded-2xl shadow-lg shadow-primary-500/30"
           >
-            <img :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
+            <img :src="siteLogo || '/logo.svg'" alt="Logo" class="h-full w-full object-contain" />
           </div>
           <h1 class="text-gradient mb-2 text-3xl font-bold">
             {{ siteName }}

frontend/src/utils/__tests__/branding.spec.ts

@@ -3,7 +3,7 @@ import { updateFavicon } from '@/utils/branding'
 
 describe('updateFavicon', () => {
   beforeEach(() => {
-    document.head.innerHTML = '<link rel="icon" href="/logo.png">'
+    document.head.innerHTML = '<link rel="icon" href="/logo.svg">'
   })
 
   it('replaces the default favicon with the configured logo', () => {
@@ -17,6 +17,6 @@ describe('updateFavicon', () => {
     updateFavicon('javascript:alert(1)')
 
     const link = document.querySelector<HTMLLinkElement>('link[rel="icon"]')
-    expect(link?.getAttribute('href')).toBe('/logo.png')
+    expect(link?.getAttribute('href')).toBe('/logo.svg')
   })
 })

frontend/src/views/HomeView.vue

@@ -42,7 +42,7 @@
         <!-- Logo -->
         <div class="flex items-center">
           <div class="h-10 w-10 overflow-hidden rounded-xl shadow-md">
-            <img :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
+            <img :src="siteLogo || '/logo.svg'" alt="Logo" class="h-full w-full object-contain" />
           </div>
         </div>
 

frontend/src/views/KeyUsageView.vue

@@ -5,7 +5,7 @@
       <nav class="mx-auto flex max-w-6xl items-center justify-between">
         <router-link to="/home" class="flex items-center gap-3">
           <div class="h-10 w-10 overflow-hidden rounded-xl shadow-md">
-            <img :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
+            <img :src="siteLogo || '/logo.svg'" alt="Logo" class="h-full w-full object-contain" />
           </div>
           <span class="text-lg font-semibold tracking-tight text-gray-900 dark:text-white">{{ siteName }}</span>
         </router-link>

frontend/src/views/public/LegalDocumentView.vue

@@ -5,7 +5,7 @@
         <RouterLink to="/home" class="flex min-w-0 items-center gap-3">
           <template v-if="settings">
             <span class="flex h-10 w-10 flex-shrink-0 items-center justify-center overflow-hidden rounded-xl bg-white shadow-sm ring-1 ring-gray-200 dark:bg-dark-800 dark:ring-dark-700">
-              <img :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
+              <img :src="siteLogo || '/logo.svg'" alt="Logo" class="h-full w-full object-contain" />
             </span>
             <span class="truncate text-base font-semibold text-gray-950 dark:text-white">
               {{ siteName }}