优化页面交互并增强 Provider 配置能力

- 表单下拉框不再用 label 包裹，改为 div + aria-label，避免点击后
  下拉面板瞬间关闭
- Provider 卡片新增「从上游获取模型」和「修改」入口，支持编辑
  base URL、API Key 与 api_mode，凭据写入对应的环境变量
- 服务端抽出 provider-model-discovery 统一不同 api_mode 的模型发现，
  旧的 custom_providers 与新的 providers 字典结构都能正确更新
- Agent Bridge 改为后台启动，HTTP 接口在 Python 运行时就绪前即可用；
  worker 连接被拒时按类型重试，不重放可能已产生副作用的请求
- 断线重连后恢复 profiles、models 与会话列表，健康检查改为自调度
  的 setTimeout，离线时 2 秒后重试
- 批量删除确认文案改用 Popconfirm content，避免变成侧栏触发器文本

tests/e2e/chat-input-dropdown.spec.ts

@@ -63,3 +63,40 @@ test('session context menu renders flat items and its export submenu', async ({
   await popup.locator('.arco-dropdown-option', { hasText: 'Export' }).click()
   await expect(page.locator('.arco-trigger-popup').filter({ hasText: 'Compressed' })).toBeVisible()
 })
+
+test('new chat selectors stay open after clicking their field and allow selection', async ({ page }) => {
+  await authenticate(page, TEST_ACCESS_KEY, 'research')
+  await mockHermesApi(page)
+  await page.route('**/api/hermes/available-models**', async route => {
+    const group = { provider: 'test-provider', label: 'Test Provider', models: ['test-model', 'other-model'] }
+    await route.fulfill({ json: {
+      default: 'test-model', default_provider: 'test-provider', groups: [group], allProviders: [group],
+      profiles: ['default', 'research'].map(profile => ({
+        profile, default: 'test-model', default_provider: 'test-provider', groups: [group],
+      })),
+    } })
+  })
+  await mockChatSocket(page)
+  await page.goto('/#/hermes/chat')
+  await page.getByRole('button', { name: 'New Chat', exact: true }).click()
+  const drawer = page.locator('.new-chat-drawer')
+  const selects = drawer.locator('.new-chat-field > .arco-select')
+  await expect(selects).toHaveCount(3)
+  await expect(selects.nth(1)).not.toHaveClass(/arco-select-disabled/)
+
+  for (const index of [0, 1, 2]) {
+    // Click the field chrome, not the internal input: a wrapping HTML label
+    // forwards this click to its input and can toggle the popup a second time.
+    await selects.nth(index).click({ position: { x: 8, y: 16 } })
+    const popup = page.locator('.arco-select-dropdown:visible')
+    await expect(popup).toBeVisible()
+    await page.waitForTimeout(300)
+    await expect(popup).toBeVisible()
+    const option = index === 0
+      ? popup.locator('.arco-select-option', { hasText: 'research' })
+      : popup.locator('.arco-select-option').first()
+    await option.click()
+    await expect(popup).toHaveCount(0)
+    await expect(drawer).toBeVisible()
+  }
+})