Re-login with the changed password in the plain-base spec

Why: phase 4 runs after the RDM phase already forced the password change,
so the initial-password attempt 401s and the sidebar never renders.

Evidence: phase-4 failure log shows the login form still up at the
15s .tsb-tool timeout; rdm-audit spec already carries this branch.

Impact: plain-base login helper mirrors rdm-audit's gate-aware login.

Refs: 2026-10-12 diagnostic report, increment 2.

e2e/plain-base.playwright.ts

@@ -28,6 +28,10 @@ async function login(page: Page) {
     await pwInputs.nth(1).fill(PASSWORD2)
     await pwInputs.nth(2).fill(PASSWORD2)
     await page.getByRole('button', { name: '设置新密码并进入' }).click()
+  } else {
+    // 已改密（RDM 阶段完成）：改用新密码重登。
+    await page.getByPlaceholder('初始密码或常用密码').fill(PASSWORD2)
+    await page.getByRole('button', { name: '登录', exact: true }).click()
   }
 }