refactor(windows): reuse packaged verifier for rollback

[testikun]

Summary

Replace the rollback verifier's private assertLaunchable CDP wrapper with the existing verifyPackagedWindowsApp authority, using the explicit legacy-baseline contract for restored pre-upgrade installations.

The rollback-specific filesystem, registry, backup, recovery, fail-closed, and .onInstFailed assertions are unchanged. The duplicate process/renderer/version plumbing is removed, and a focused harness test pins the delegation contract.

Fixes #3575

Verification

• node --test scripts/verify-windows-harness.test.mjs — 40 passed
• npm --workspace @maka/eval run build — passed (required release-test fixture)
• node --test scripts/product-release.test.mjs scripts/verify-windows-harness.test.mjs — 66 passed
• npm run lint — passed
• npx biome check scripts/verify-windows-installer-rollback.mjs scripts/verify-windows-harness.test.mjs — passed
• node --check for both changed scripts and git diff --check — passed
• The real Windows installer rollback gate was not run locally because this workspace is macOS; it remains the authoritative Windows CI check.
• The repository-wide npm run typecheck currently reports unrelated errors in unmodified Runtime Host, CLI, UI, and Desktop files on the latest main.

中文摘要

本 PR 复用已有的 packaged-app verifier 来验证回滚后的旧版本安装，固定使用 legacy-baseline 契约，删除重复的 CDP/进程/版本检查代码；所有备份、注册表、失败恢复和 .onInstFailed 回滚行为保持不变，并补充了 delegation 回归测试。

AI use

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Tool: OpenAI Codex assisted with issue analysis, implementation, tests, and verification.