feat: 添加浏览器标签图标 favicon

- 创建 SVG 格式 favicon（深色背景+大脑/网络节点设计）
- 在所有后台管理页面添加 favicon

admin/static/img/favicon.svg

@@ -0,0 +1,12 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect x="2" y="2" width="28" height="28" rx="4" fill="#1a1a2e"/>
+  <circle cx="16" cy="16" r="10" fill="#4a90d9" opacity="0.3"/>
+  <path d="M16 6 L16 10 M16 22 L16 26 M6 16 L10 16 M22 16 L26 16" stroke="#4a90d9" stroke-width="2"/>
+  <circle cx="16" cy="16" r="6" fill="#4a90d9"/>
+  <path d="M12 14 L16 16 L20 14 M12 18 L16 16 L20 18" stroke="#fff" stroke-width="1.5" fill="none"/>
+  <circle cx="10" cy="10" r="2" fill="#28a745"/>
+  <circle cx="22" cy="10" r="2" fill="#28a745"/>
+  <circle cx="10" cy="22" r="2" fill="#28a745"/>
+  <circle cx="22" cy="22" r="2" fill="#28a745"/>
+  <path d="M10 10 L16 16 M22 10 L16 16 M10 22 L16 16 M22 22 L16 16" stroke="#28a745" stroke-width="1" opacity="0.5"/>
+</svg>

admin/templates/auto-profiles.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Auto配置管理 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/chat.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>对话 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/config.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>系统配置 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/index.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>LLM Proxy - 后台管理</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/logs.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>日志查看 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/models.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>模型管理 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>

admin/templates/providers.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>提供商管理 - LLM Proxy</title>
+    <link rel="icon" href="/static/img/favicon.svg" type="image/svg+xml">
     <script src="https://cdn.tailwindcss.com"></script>
     <link href="https://cdn.jsdelivr.net/npm/remixicon@3.5.0/fonts/remixicon.css" rel="stylesheet">
     <style>