docs: sync agent teams monitoring guidance

[kaitranntt]

Summary

• Update public /ck:team docs in English and Vietnamese to describe explicit TaskList/message monitoring instead of default event-driven hook automation.
• Move the retired Agent Teams handler filenames into the removed-hooks guidance.
• Clarify that TaskCompleted and TeammateIdle remain Claude Code platform events, but ClaudeKit does not register default handlers for them.
• Add minimal null guards in existing UI scripts so the required astro check gate passes.

Validation

• bunx astro check
• bun test tests/
• bun run check:syntax (warn-only; reports pre-existing unrelated colon-syntax warnings)
• bun run build
• bun run check:sitemap
• git diff --check

Supports claudekit-engineer#806.