fix(web): 项目主图标统一替换为昔涟3rd_Form-Cyrene-3F-Q-Happy-1.png

- favicon/apple-touch-icon (index.html)
- PWA manifest 图标 (manifest.json)
- PWA precache (sw.js)
- 用户端侧栏品牌头像 (Nav.tsx)
- 管理面板顶栏品牌头像 (AdminApp.tsx)
- 删除已被替换的 icon.svg 残留引用

frontend/web/public/icon.svg

@@ -1,11 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48" width="48" height="48">
-  <defs>
-    <linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
-      <stop offset="0" stop-color="#3d6bff" />
-      <stop offset="1" stop-color="#6a8dff" />
-    </linearGradient>
-  </defs>
-  <rect x="4" y="4" width="40" height="40" rx="12" fill="url(#g)" />
-  <circle cx="24" cy="24" r="10" fill="#0c0c0c" />
-  <circle cx="24" cy="24" r="4" fill="#f5f5f7" />
-</svg>

frontend/web/public/manifest.json

@@ -9,10 +9,10 @@
   "orientation": "any",
   "icons": [
     {
-      "src": "/icon.svg",
-      "type": "image/svg+xml",
-      "sizes": "any",
-      "purpose": "any maskable"
+      "src": "/images/Cyrene_Avatar/3rd_Form/Cyrene-3F-Q-Happy-1.png",
+      "type": "image/png",
+      "sizes": "1500x1500",
+      "purpose": "any"
     }
   ]
 }

frontend/web/public/sw.js

@@ -1,6 +1,6 @@
 /* Cyrene v2 PWA service worker — core-resource caching + offline shell. */
 const CACHE = "cyrene-web-v1";
-const PRECACHE = ["/", "/index.html", "/manifest.json", "/icon.svg"];
+const PRECACHE = ["/", "/index.html", "/manifest.json", "/images/Cyrene_Avatar/3rd_Form/Cyrene-3F-Q-Happy-1.png"];
 
 self.addEventListener("install", (event) => {
   event.waitUntil(