feat(updater): add versioned release announcements

[Is14w]

Linked issue

Closes #832

Summary

• Show the installed version's GitHub Release notes on the first launch after an app version change.
• Persist acknowledgement per version while keeping close / view-later actions session-local, and allow reopening the current announcement from Settings -> About.
• Add a development-only preview action for the latest Release without mutating acknowledgement state; release builds omit both the UI entry and the backend debug command.
• Render the announcement with the existing Markdown and dialog primitives, localized for Chinese and English.

Change scope

• Modules: agent-gui, agent-gui/src-tauri, desktop release documentation
• Key paths:
  • crates/agent-gui/src-tauri/src/commands/app/update.rs
  • crates/agent-gui/src/lib/releaseAnnouncement.ts
  • crates/agent-gui/src/lib/releaseNotes.ts
  • crates/agent-gui/src/components/ReleaseAnnouncementDialog.tsx
  • crates/agent-gui/src/pages/settings/AboutSection.tsx
  • crates/agent-gui/src/i18n/config.ts
  • crates/agent-gui/test/settings/release-announcement.test.mjs
  • docs/operations/deployment.md

Screenshots / preview

Runtime preview:

1. Run cd crates/agent-gui && pnpm tauri dev.
2. Open Settings -> About.
3. Under Debug Mode, select Preview Update Announcement.
4. Confirm that closing the preview does not change the installed version's acknowledgement state.

Verification

• cd crates/agent-gui && pnpm typecheck
• cd crates/agent-gui && pnpm build
• cd crates/agent-gui && node --test test/settings/release-announcement.test.mjs test/i18n/translations.test.mjs (12 passed)
• cargo test --manifest-path crates/agent-gui/src-tauri/Cargo.toml current_release --lib (2 passed)
• cd crates/agent-gui && pnpm exec biome check src/App.tsx src/agent-ui-adapters/settingsExtension.tsx src/components/ReleaseAnnouncementDialog.tsx src/i18n/config.ts src/lib/releaseAnnouncement.ts src/lib/releaseNotes.ts src/pages/settings/AboutSection.tsx src/pages/settings/types.ts
• git diff --check

Pre-submit checklist

• A requirement issue is linked (or this is a trivial fix that needs no issue, as explained in the summary).
• Synced with the target branch; no merge conflicts.
• The change is focused, with no unrelated modifications.
• No secrets, tokens, or personal data included.
• Docs are updated for changes affecting user behavior, deployment, or configuration.