docs: sync to Claude Code v2.1.126 (six new releases since April 27) (#111)

Bumps tutorial coverage from v2.1.119 → v2.1.126 (May 1, 2026 release).
v2.1.120 was rolled back on its first release day (2026-04-24) but
re-released 2026-04-28 with regressions fixed; v2.1.124/125 skipped.

New feature documentation:
- claude project purge (v2.1.126) — 10-cli
- claude plugin prune / --prune (v2.1.121) — 07-plugins, 10-cli
- claude ultrareview [target] (v2.1.120) — 10-cli
- ${CLAUDE_EFFORT} placeholder + type-to-filter /skills (v2.1.120-121) — 03-skills
- alwaysLoad MCP server config option (v2.1.121) — 05-mcp
- PostToolUse.updatedToolOutput for non-MCP tools (v2.1.121) — 06-hooks
- ANTHROPIC_BEDROCK_SERVICE_TIER, AI_AGENT env vars — 10-cli
- --dangerously-skip-permissions extended path coverage — 09-advanced-features
- Windows PowerShell-as-primary-shell + /model gateway discovery (v2.1.126)
- OAuth code paste fallback (v2.1.126) — 10-cli

Fixes:
- xhigh missing from 03-skills effort enum (regression from April 24)
- README.md latest-version claims (lines 105, 204) and version badge
- CHANGELOG.md v2.4.0 stale "v2.1.120 was rolled back" paragraph

Footer refresh: 22 in-scope English files bumped to May 2, 2026 / 2.1.126.
Localized vi/zh/uk/ja trees out of scope (community-maintained).

01-slash-commands/README.md

@@ -601,8 +601,8 @@ If both exist with the same name, the **skill takes precedence**. Remove one or
 
 ---
 
-**Last Updated**: April 24, 2026
-**Claude Code Version**: 2.1.119
+**Last Updated**: May 2, 2026
+**Claude Code Version**: 2.1.126
 **Sources**:
 - https://code.claude.com/docs/en/slash-commands
 - https://code.claude.com/docs/en/interactive-mode