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.

03-skills/README.md

@@ -95,6 +95,8 @@ sequenceDiagram
 
 When skills share the same name across levels, higher-priority locations win: **enterprise > personal > project**. Plugin skills use a `plugin-name:skill-name` namespace, so they cannot conflict.
 
+> **Subagent skill discovery (v2.1.133+)**: Subagents now discover project, user, and plugin skills via the Skill tool the same way the main session does. Earlier versions limited subagents to their own embedded set, which meant skill+subagent workflows quietly degraded; from v2.1.133 the same skill catalog is visible to both.
+
 ### Automatic Discovery
 
 **Nested directories**: When you work with files in subdirectories, Claude Code automatically discovers skills from nested `.claude/skills/` directories. For example, if you're editing a file in `packages/frontend/`, Claude Code also looks for skills in `packages/frontend/.claude/skills/`. This supports monorepo setups where packages have their own skills.
@@ -844,8 +846,8 @@ Once you start building skills seriously, two things become essential: a library
 - [Hooks Guide](../06-hooks/) - Event-driven automation
 
 ---
-**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/skills
 - https://code.claude.com/docs/en/settings