chore(desktop): prepare 1.4.2 release

[lxrzlyr]

Summary

• set the Desktop package and workspace lock version to 1.4.2
• align the public English, Chinese, and design documentation to DeepAgent Core V4.0.4
• correct the Chinese installation and quick-start commands

Verification

• bun typecheck in packages/desktop
• bun test src/main/updater-controller.test.ts src/main/updater-subscriptions.test.ts in packages/desktop (8 passed)
• repository pre-push bun turbo typecheck (15 packages passed)
• release-version consistency assertions and git diff --check

Release behavior

A subsequent push of the integrated release commit to main will let desktop-build.yml publish app-v1.4.2-main.<run> as the latest updater release.

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