Self-skip the plain-base spec outside its e2e phase

Why: the phase-3 playwright run scans the whole e2e/ directory, so the
plain-base assertions ran against the RDM combo where the audit entry is
legitimately visible and failed.

Evidence: phase-3 rerun shows 4 rdm-audit tests passing with plain-base
failing out of place; the spec now skips unless E2E_PLAIN_BASE=1, which
scripts/e2e.sh phase 4 injects.

Impact: plain-base scenario only executes against the plain base serve.

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

e2e/plain-base.playwright.ts

@@ -9,7 +9,10 @@ const OWNER = process.env.E2E_OWNER || 'e2e-auditor'
 const PASSWORD = process.env.E2E_PASSWORD || 'E2eAudit#2026'
 const PASSWORD2 = process.env.E2E_PASSWORD2 || 'E2eAudit#2026b'
 
-test.skip(!process.env.PLAYWRIGHT_BASE_URL, 'set PLAYWRIGHT_BASE_URL (scripts/e2e.sh drives this suite)')
+// 仅第 4 阶段（普通基座）启用：RDM 组合主跑（第 3 阶段）扫全目录时本文件自跳过，
+// 否则「入口隐藏」断言会跑在入口本就可见的 RDM 组合上。
+test.skip(!(process.env.PLAYWRIGHT_BASE_URL && process.env.E2E_PLAIN_BASE),
+  'set PLAYWRIGHT_BASE_URL + E2E_PLAIN_BASE (scripts/e2e.sh phase 4 drives this suite)')
 
 // 与 rdm-audit spec 同一账号：若数据库仍是初始密码则先过强制改密门。
 async function login(page: Page) {