feat(anthropic): 支持 API Key 自动透传并优化透传链路性能

- 新增 Anthropic API Key 自动透传开关与后端透传分支（仅替换认证）

- 账号编辑页新增自动透传开关，默认关闭

- 优化透传性能：SSE usage 解析 gjson 快路径、减少请求体重复拷贝、优化流式写回与非流式 usage 解析

- 补充单元测试与 benchmark，确保 Claude OAuth 路径不受影响

frontend/src/components/account/EditAccountModal.vue

@@ -735,6 +735,36 @@
         </div>
       </div>
 
+      <!-- Anthropic API Key 自动透传开关 -->
+      <div
+        v-if="account?.platform === 'anthropic' && account?.type === 'apikey'"
+        class="border-t border-gray-200 pt-4 dark:border-dark-600"
+      >
+        <div class="flex items-center justify-between">
+          <div>
+            <label class="input-label mb-0">{{ t('admin.accounts.anthropic.apiKeyPassthrough') }}</label>
+            <p class="mt-1 text-xs text-gray-500 dark:text-gray-400">
+              {{ t('admin.accounts.anthropic.apiKeyPassthroughDesc') }}
+            </p>
+          </div>
+          <button
+            type="button"
+            @click="anthropicPassthroughEnabled = !anthropicPassthroughEnabled"
+            :class="[
+              'relative inline-flex h-6 w-11 flex-shrink-0 cursor-pointer rounded-full border-2 border-transparent transition-colors duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-primary-500 focus:ring-offset-2',
+              anthropicPassthroughEnabled ? 'bg-primary-600' : 'bg-gray-200 dark:bg-dark-600'
+            ]"
+          >
+            <span
+              :class="[
+                'pointer-events-none inline-block h-5 w-5 transform rounded-full bg-white shadow ring-0 transition duration-200 ease-in-out',
+                anthropicPassthroughEnabled ? 'translate-x-5' : 'translate-x-0'
+              ]"
+            />
+          </button>
+        </div>
+      </div>
+
       <!-- OpenAI OAuth Codex 官方客户端限制开关 -->
       <div
         v-if="account?.platform === 'openai' && account?.type === 'oauth'"
@@ -1223,6 +1253,7 @@ const cacheTTLOverrideTarget = ref<string>('5m')
 // OpenAI 自动透传开关（OAuth/API Key）
 const openaiPassthroughEnabled = ref(false)
 const codexCLIOnlyEnabled = ref(false)
+const anthropicPassthroughEnabled = ref(false)
 const isOpenAIModelRestrictionDisabled = computed(() =>
   props.account?.platform === 'openai' && openaiPassthroughEnabled.value
 )
@@ -1317,12 +1348,16 @@ watch(
       // Load OpenAI passthrough toggle (OpenAI OAuth/API Key)
       openaiPassthroughEnabled.value = false
       codexCLIOnlyEnabled.value = false
+      anthropicPassthroughEnabled.value = false
       if (newAccount.platform === 'openai' && (newAccount.type === 'oauth' || newAccount.type === 'apikey')) {
         openaiPassthroughEnabled.value = extra?.openai_passthrough === true || extra?.openai_oauth_passthrough === true
         if (newAccount.type === 'oauth') {
           codexCLIOnlyEnabled.value = extra?.codex_cli_only === true
         }
       }
+      if (newAccount.platform === 'anthropic' && newAccount.type === 'apikey') {
+        anthropicPassthroughEnabled.value = extra?.anthropic_passthrough === true
+      }
 
       // Load antigravity model mapping (Antigravity 只支持映射模式)
       if (newAccount.platform === 'antigravity') {
@@ -1882,6 +1917,18 @@ const handleSubmit = async () => {
       updatePayload.extra = newExtra
     }
 
+    // For Anthropic API Key accounts, handle passthrough mode in extra
+    if (props.account.platform === 'anthropic' && props.account.type === 'apikey') {
+      const currentExtra = (props.account.extra as Record<string, unknown>) || {}
+      const newExtra: Record<string, unknown> = { ...currentExtra }
+      if (anthropicPassthroughEnabled.value) {
+        newExtra.anthropic_passthrough = true
+      } else {
+        delete newExtra.anthropic_passthrough
+      }
+      updatePayload.extra = newExtra
+    }
+
     // For OpenAI OAuth/API Key accounts, handle passthrough mode in extra
     if (props.account.platform === 'openai' && (props.account.type === 'oauth' || props.account.type === 'apikey')) {
       const currentExtra = (props.account.extra as Record<string, unknown>) || {}

frontend/src/i18n/locales/en.ts

@@ -1546,6 +1546,11 @@ export default {
         enableSora: 'Enable Sora simultaneously',
         enableSoraHint: 'Sora uses the same OpenAI account. Enable to create Sora account simultaneously.'
       },
+      anthropic: {
+        apiKeyPassthrough: 'Auto passthrough (auth only)',
+        apiKeyPassthroughDesc:
+          'Only applies to Anthropic API Key accounts. When enabled, messages/count_tokens are forwarded in passthrough mode with auth replacement only, while billing/concurrency/audit and safety filtering are preserved. Disable to roll back immediately.'
+      },
       modelRestriction: 'Model Restriction (Optional)',
       modelWhitelist: 'Model Whitelist',
       modelMapping: 'Model Mapping',

frontend/src/i18n/locales/zh.ts

@@ -1694,6 +1694,11 @@ export default {
         enableSora: '同时启用 Sora',
         enableSoraHint: 'Sora 使用相同的 OpenAI 账号，开启后将同时创建 Sora 平台账号'
       },
+      anthropic: {
+        apiKeyPassthrough: '自动透传（仅替换认证）',
+        apiKeyPassthroughDesc:
+          '仅对 Anthropic API Key 生效。开启后，messages/count_tokens 请求将透传上游并仅替换认证，保留计费/并发/审计及必要安全过滤；关闭即可回滚到现有兼容链路。'
+      },
       modelRestriction: '模型限制（可选）',
       modelWhitelist: '模型白名单',
       modelMapping: '模型映射',