docs: sync all tutorials with latest Claude Code docs (April 2026) (#56)

* docs: sync all tutorials with latest Claude Code official docs (April 2026)

Update 44 documentation files to reflect the latest Claude Code features
from code.claude.com. Key content changes include new slash commands
(/ultraplan, /powerup, /sandbox), deprecated command removals (/pr-comments,
/vim), corrected skill description budget (1%/8K), new hook events
(PermissionDenied, InstructionsLoaded, ConfigChange), expanded Agent Teams
section, new plugin components (LSP, bin/, settings.json), and new CLI
flags (--bare, --tmux, --effort, --channels). Added "Last Updated: April
2026" metadata footer to all documentation files.

* fix(docs): correct env var values and alphabetical ordering

- CLAUDE_CODE_NEW_INIT=true → =1 in 02-memory and 09-advanced-features
- CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=true → =1 in 09-advanced-features
- Fix /powerup vs /plugin alphabetical order in slash commands table

* fix(docs): correct env var values in locale files (vi, zh)

Propagate CLAUDE_CODE_NEW_INIT=true → =1 and
CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=true → =1 corrections
to Vietnamese and Chinese translations.

QUICK_REFERENCE.md

@@ -504,3 +504,7 @@ Getting started checklist:
 **Full Index**: `cat INDEX.md`
 
 **This Card**: Keep it handy for quick reference!
+
+---
+**Last Updated**: April 2026
+**Claude Code Version**: 2.1+