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

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "repo-standard",
-  "version": "0.2.1",
+  "version": "0.2.2",
   "description": "Per-repo gate for the open/ presentation standard: README first screen, install block, files required by the repo's class, and dead repo references.",
   "author": {
     "name": "Kjell Tore Guttormsen"