feat: E2E 测试集成真实后端

- Playwright 双 webServer 模式自动启动 Go 后端 + Vite 前端
- 后端使用临时 SQLite 数据库隔离，固定端口 19026
- vite.config.ts proxy target 动态读取环境变量
- 新增 sql.js 依赖用于 SQLite 统计数据 seed
- 新增 e2e/fixtures.ts 共享工具模块（API seed + SQLite seed）
- 拆分测试文件 5→7（providers/models/stats/navigation/validation）
- 删除旧文件 crud.spec.ts/sidebar.spec.ts/stats-cards.spec.ts
- E2E 测试尚有部分用例需调试修复

frontend/e2e/fixtures.ts

@@ -0,0 +1,87 @@
+import fs from 'node:fs'
+import path from 'node:path'
+import initSqlite from 'sql.js'
+
+export const API_BASE = `http://localhost:${process.env.NEX_BACKEND_PORT || '19026'}`
+
+export interface SeedProviderInput {
+  id: string
+  name: string
+  apiKey: string
+  baseUrl: string
+  protocol: 'openai' | 'anthropic'
+  enabled: boolean
+}
+
+export interface SeedModelInput {
+  providerId: string
+  modelName: string
+  enabled: boolean
+}
+
+export interface SeedStatsInput {
+  providerId: string
+  modelName: string
+  requestCount: number
+  date: string
+}
+
+export async function seedProvider(
+  request: import('@playwright/test').APIRequestContext,
+  data: SeedProviderInput,
+) {
+  const resp = await request.post(`${API_BASE}/api/providers`, {
+    data: {
+      id: data.id,
+      name: data.name,
+      api_key: data.apiKey,
+      base_url: data.baseUrl,
+      protocol: data.protocol,
+      enabled: data.enabled,
+    },
+  })
+  if (!resp.ok()) {
+    throw new Error(`seedProvider failed: ${resp.status()} ${await resp.text()}`)
+  }
+  return resp.json()
+}
+
+export async function seedModel(
+  request: import('@playwright/test').APIRequestContext,
+  data: SeedModelInput,
+) {
+  const resp = await request.post(`${API_BASE}/api/models`, {
+    data: {
+      provider_id: data.providerId,
+      model_name: data.modelName,
+      enabled: data.enabled,
+    },
+  })
+  if (!resp.ok()) {
+    throw new Error(`seedModel failed: ${resp.status()} ${await resp.text()}`)
+  }
+  return resp.json()
+}
+
+export async function seedUsageStats(statsData: SeedStatsInput[]) {
+  const tempDir = process.env.NEX_E2E_TEMP_DIR
+  if (!tempDir) {
+    throw new Error('NEX_E2E_TEMP_DIR not set')
+  }
+
+  const dbPath = path.join(tempDir, 'test.db')
+  const SQL = await initSqlite()
+  const buf = fs.readFileSync(dbPath)
+  const db = new SQL.Database(buf)
+
+  for (const row of statsData) {
+    db.run(
+      'INSERT OR REPLACE INTO usage_stats (provider_id, model_name, request_count, date) VALUES (?, ?, ?, ?)',
+      [row.providerId, row.modelName, row.requestCount, row.date],
+    )
+  }
+
+  const data = db.export()
+  fs.writeFileSync(dbPath, Buffer.from(data))
+  db.close()
+}