chore: prepare GoAgent v0.4.19 release

[wimi321]

Summary

Prepares GoAgent v0.4.19 after merging the first-run onboarding and persistent Zhizi Cloud analysis work.

Release highlights

• one-time onboarding that follows the system language
• optional AI teacher setup with text, image, and tool-call verification
• cancellable 30-second background KataGo benchmark and resumable model downloads
• persistent Zhizi Cloud Socket.IO/GTP analysis with live speed, cancellation, retry, and idle release
• local KataGo remains the default; remote compute requires explicit successful enablement
• official Zhizi app entry for account and subscription management
• seven-language release notes with links to all six published desktop assets

Release-quality contract

The release-note contract now mirrors the real workflow: both installer and portable Windows assets must be linked, while retired Lite and split NVIDIA artifacts remain forbidden.

Verification

• pnpm install --frozen-lockfile
• pnpm test (226/226)
• pnpm typecheck
• pnpm build
• pnpm check:teacher-quality
• pnpm check:website
• pnpm check:p0-beta
• pnpm rc:check
• pnpm check:artifacts
• pnpm check:release-quality

Kokoro strict asset validation remains a release-job gate: the CI release workflow downloads the ONNX assets, validates them strictly, and blocks publication if preparation or synthesis smoke fails.

The local website/design-concepts/ directory is intentionally excluded.