feat: API Key 前缀改为 sk-ot

- apikey 包 prefix 常量 sk- → sk-ot（生成/校验/展示前缀统一驱动）
- 鉴权错误提示同步更新为 sk-ot 格式
- 测试断言改用常量，避免硬编码长度
- 前端 curl 示例与 README/PLANNING 文档同步

web/src/views/LandingView.vue

@@ -79,7 +79,7 @@ const baseURL = `${window.location.origin}/v1`
           <div class="space-y-3 p-4 leading-relaxed">
             <div>
               <p class="text-muted"><span class="text-accent">$</span> curl {{ baseURL }}/chat/completions</p>
-              <p class="text-muted">  -H <span class="text-accent">"Authorization: Bearer sk-..."</span> \</p>
+              <p class="text-muted">  -H <span class="text-accent">"Authorization: Bearer sk-ot..."</span> \</p>
               <p class="text-muted">  -d <span class="text-ink">'{"model": "claude-sonnet-5", "messages": [{"role": "user", "content": "你好"}]}'</span></p>
             </div>
             <div class="border-t border-edge pt-3 text-muted">
@@ -136,7 +136,7 @@ const baseURL = `${window.location.origin}/v1`
             </p>
           </div>
           <div class="card p-5">
-            <p class="font-mono text-xs text-muted">sk-…</p>
+            <p class="font-mono text-xs text-muted">sk-ot…</p>
             <h3 class="mt-2 text-lg font-semibold">API Key 管理</h3>
             <p class="mt-2 text-sm leading-relaxed text-muted">
               密钥仅存哈希，支持配额、过期与模型白名单，创建时一次性展示。

web/src/views/console/DashboardView.vue

@@ -49,7 +49,7 @@ function daysAgo(n: number): string {
 // 快速开始：Base URL 用浏览器当前 host（兼容端点），curl 示例
 const baseURL = `${window.location.origin}/v1`
 const curlCmd = `curl ${baseURL}/chat/completions \\
-  -H "Authorization: Bearer sk-xxxx" \\
+  -H "Authorization: Bearer sk-ot-xxxx" \\
   -H "Content-Type: application/json" \\
   -d '{"model":"gpt-test","stream":true,"messages":[{"role":"user","content":"hi"}]}'`
 const copied = ref('')