fix: preserve official Zhizi account guidance

[wimi321]

Summary

Reconciles the only user-facing capability from the superseded Zhizi PR #14 that was not already covered by the newer persistent-engine implementation.

• Adds a safe main-process action for opening the verified official Zhizi app download page.
• Adds the entry to the current persistent Zhizi settings flow.
• Localizes the action and guidance in all seven supported UI languages.
• Keeps local KataGo as the default and preserves explicit probe-before-enable behavior.
• Does not restore the legacy short-lived engine, login-auto-enable behavior, or obsolete compute-tier mapping.

Verification

• curl -I -L https://zhizigo.com/download (HTTP 200)
• node --test tests/zhizi-cloud-engine-contract.test.mjs tests/ui-i18n-contract.test.mjs
• pnpm typecheck
• pnpm build
• git diff --check

Supersedes the remaining unique scope of #14.