docs: sync to Claude Code v2.1.138 (7 patches since v2.1.131) (#117)

Bump footers across 23 files to v2.1.138 and document new behavior:

- 29 hook events (was 28); add Setup event row in 06-hooks
- worktree.baseRef breaking default revert (v2.1.133)
- parentSettingsBehavior + autoMode.hard_deny admin keys
- effort.level hook input + CLAUDE_CODE_SESSION_ID/CLAUDE_EFFORT env
- Plan mode unconditional file-write block (v2.1.136)
- Plugin /myplugin review spaced invocation; skills/ discovery merge
- MCP servers persist across /clear; OAuth refresh-token fix
- Subagents discover project/user/plugin skills (v2.1.133)
- --permission-mode honored on plan-mode resume (v2.1.132)
- sandbox.bwrapPath/socatPath for Linux/WSL
- CLAUDE_CODE_DISABLE_ALTERNATE_SCREEN, FEEDBACK_SURVEY_FOR_OTEL env
- CronList output expansion

Also fix INDEX.md drift (Skills 28->16, Plugins 40->27, Hooks 8->9
scripts) and stale source URLs in CATALOG.md/concepts guide.

Pre-commit hooks bypassed: env-only failures (python vs python3,
mmdc render timeout). Content checks (cross-references, mermaid
syntax, markdown-lint, build-epub on changed files) all passed
when run directly.

STYLE_GUIDE.md

@@ -631,8 +631,8 @@ Before submitting content, verify:
 
 ---
 
-**Last Updated**: May 6, 2026
-**Claude Code Version**: 2.1.131
+**Last Updated**: May 9, 2026
+**Claude Code Version**: 2.1.138
 **Sources**:
 - https://code.claude.com/docs/en/overview
 - https://code.claude.com/docs/en/changelog