docs: sync to Claude Code v2.1.101 with /team-onboarding, /ultraplan, Monitor tool (#73)

* docs: sync to Claude Code v2.1.101 with new feature coverage

Bumps all English docs from v2.1.97 to v2.1.101, adds mandatory Sources
footer block (previously missing), and documents three new features
shipped between v2.1.98 and v2.1.101:

- /team-onboarding (v2.1.101) — new built-in command for generating
  teammate ramp-up guides. Added to 01-slash-commands and CATALOG.
- /ultraplan (v2.1.91+, cloud-env auto-creation in v2.1.101) — full
  section in 09-advanced-features covering launch methods, status
  indicators, and execution options. Replaces prior 3-line stub.
- Monitor tool (v2.1.98) — full section in 09-advanced-features with
  stream-filter and poll-emit patterns and the grep --line-buffered
  warning. Added to resources.md feature table.

Vietnamese and Chinese translations are not touched in this sync.

* fix(docs): address review feedback on v2.1.101 sync

- Correct /team-onboarding availability date (April 10 → April 11, 2026)
- Fix uninitialized \$last variable in Monitor poll-and-emit example
- Update CATALOG.md New Features heading to April 2026 and add Monitor
  Tool, /team-onboarding, and Ultraplan auto-create entries

07-plugins/README.md

@@ -944,6 +944,8 @@ The following Claude Code features work together with plugins:
 - [Hook System Reference](../06-hooks/README.md)
 
 ---
-**Last Updated**: April 9, 2026
-**Claude Code Version**: 2.1.97
+**Last Updated**: April 11, 2026
+**Claude Code Version**: 2.1.101
+**Sources**:
+- https://code.claude.com/docs/en/plugins
 **Compatible Models**: Claude Sonnet 4.6, Claude Opus 4.6, Claude Haiku 4.5