feat: 三协议互转网关 + 鉴权修复 + 管理端增强

后端
- 新增 proxy/convert 三协议（chat/messages/responses）请求、响应与 SSE 流式互转，
  以 Chat 为中间模型；usage.go 统一提取三协议 token 用量（含单测）
- gateway: 跨协议调度（渠道未声明客户端协议时转为渠道首选格式），
  streamResponse 按 \n\n 分块逐行转换直通，bufferResponse 转换失败时剥非 JSON 前缀
- gateway: 新增 SetUsageRecorder 注入异步用量记录器
- auth_llm: 修复 key_prefix 查询长度错配（[:8] vs 存储的 [:12]）导致全部 401；
  修复长度 8-11 的 key 切片越界 panic；统一 unauthorized 响应
- usage: 日报表改为增量累加 upsert，避免多次 flush 互相清零；记录协议/错误码/时延等字段
- channel: 新增渠道并发槽 TryAcquire；健康检查支持可配置参数
- api: 新增 admin 渠道/模型/系统配置管理端点（旧端点保留兼容）

前端
- 新增渠道管理、模型管理、系统配置视图与 ChannelModelsDrawer
- 新增 ui 基础组件（Button/Badge/Input/Modal）与 protocol.ts
- 调整 Toast 样式、密钥页、路由菜单；dev 代理默认指向 3000 端口

frontend/src/components/ui/Modal.vue

@@ -0,0 +1,84 @@
+<script setup lang="ts">
+import { nextTick, onMounted, onUnmounted, ref, watch } from 'vue'
+import { X } from '@lucide/vue'
+
+const props = withDefaults(
+  defineProps<{
+    open: boolean
+    title?: string
+    width?: string
+  }>(),
+  { width: 'max-w-md' },
+)
+const emit = defineEmits<{ close: [] }>()
+
+const panel = ref<HTMLElement | null>(null)
+
+function onKey(e: KeyboardEvent) {
+  if (e.key === 'Escape' && props.open) emit('close')
+}
+onMounted(() => window.addEventListener('keydown', onKey))
+onUnmounted(() => window.removeEventListener('keydown', onKey))
+
+watch(
+  () => props.open,
+  async (open) => {
+    document.body.style.overflow = open ? 'hidden' : ''
+    if (open) {
+      await nextTick()
+      panel.value?.focus()
+    }
+  },
+)
+onUnmounted(() => {
+  document.body.style.overflow = ''
+})
+</script>
+
+<template>
+  <Teleport to="body">
+    <Transition
+      enter-active-class="transition-opacity duration-150"
+      enter-from-class="opacity-0"
+      leave-active-class="transition-opacity duration-150"
+      leave-to-class="opacity-0"
+    >
+      <div
+        v-if="open"
+        class="fixed inset-0 z-50 flex items-start justify-center overflow-y-auto bg-black/60 p-4 pt-[12vh] backdrop-blur-sm"
+        @mousedown.self="emit('close')"
+      >
+        <Transition
+          enter-active-class="transition-transform duration-150"
+          enter-from-class="scale-[0.97] opacity-0"
+          leave-active-class="transition-transform duration-150"
+          leave-to-class="scale-[0.97] opacity-0"
+        >
+          <div
+            v-if="open"
+            ref="panel"
+            role="dialog"
+            aria-modal="true"
+            :aria-label="title || '对话框'"
+            tabindex="-1"
+            class="card w-full bg-base-100 shadow-xl outline-none"
+            :class="width"
+          >
+            <div class="flex items-center justify-between border-b border-base-300/60 px-5 py-3.5">
+              <h3 class="text-sm font-semibold text-base-content">{{ title }}</h3>
+              <button class="rounded-md p-1 text-base-content/40 hover:bg-base-200 hover:text-base-content" aria-label="关闭" @click="emit('close')">
+                <X :size="16" />
+              </button>
+            </div>
+            <div class="px-5 py-4">
+              <slot />
+            </div>
+            <div v-if="$slots.footer" class="flex justify-end gap-2 border-t border-base-300/60 px-5 py-3.5">
+              <slot name="footer" />
+            </div>
+          </div>
+        </Transition>
+      </div>
+    </Transition>
+  </Teleport>
+</template>