fix(engine): print engine version, so a stale plugin cache is visible

Measured 2026-08-04: two repos (llm-security, config-audit) independently
proved the /repo-standard skill had resolved ${CLAUDE_PLUGIN_ROOT} to a
cached 0.1.1 while 0.2.0 was installed and the catalog pinned it — same
instruction, same variable, wrong engine. 0.1.1 has neither BADGE-COUNT nor
README-LANGUAGE, so a broadcast recommending the skill produced clean-looking
runs that could not have found what they were sent to find.

The header line and --json output now carry `repo-standard v<version>`
(headerLine/withEngineVersion, both pure and unit tested). SKILL.md tells the
reader to confirm it against the catalog pin before trusting green. The
stale-cache resolution itself is the harness's, not this repo's — not fixed
here, only made visible instead of silent.

TDD: 4 new tests. 111/111 green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01496ZWasKPnA627crFBXWhe

CHANGELOG.md

@@ -4,6 +4,20 @@ All notable changes to this project are documented here.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/);
 versioning is [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.2] — 2026-08-04
+
+### Fixed
+
+- The engine never printed its own version, which is how a stale plugin cache
+  went unnoticed: two repos independently proved the `/repo-standard` skill
+  had resolved `${CLAUDE_PLUGIN_ROOT}` to a cached `0.1.1` while `0.2.0` was
+  installed and the catalog pinned it — same instruction, wrong engine, and
+  `0.1.1` has neither `BADGE-COUNT` nor `README-LANGUAGE`, so the run looked
+  clean instead of incomplete. The header line and `--json` output now both
+  carry `repo-standard v<version>`; `SKILL.md` tells the reader to confirm it
+  against the catalog pin before trusting a green result. The cache
+  resolution itself is the harness's, not this repo's, and is not fixed here.
+
 ## [0.2.1] — 2026-08-04
 
 ### Fixed