feat(engine)!: "no version to compare against" is a verdict, not a skip

`VERSION-UNAVAILABLE` (SKIP/notRun) becomes `VERSION-NONE` (OK). A repo that
claims no version in any of the four places one can be written down has not
left a check un-run — the check ran, saw all four, and found no subject. That
is the shape `checkReadmeLanguage` has always answered with OK.

0.8.0 deferred this and recorded the reason in the engine: re-levelling "moves
a repo's status". Measured false across 19 clones — an added OK cannot worsen
the worst *judged* finding, and all three repos emitting the code already read
OK. Status moves only for a repo whose entire finding set was skips.

OK cannot bless a real gap here: no class requires a version file, and a
`plugin` missing its manifest is an independent FILE-MISSING ERROR.

Renamed, not just re-levelled: `-UNAVAILABLE` is this engine's naming for a
notRun skip, and one OK-level `-UNAVAILABLE` would mislead exactly the reader
this change serves. A source scan keeps the old name out.

A/B sweep, both engines offline, 19 clones: 223 judged findings, every status
and buckets identical; 3 conversions (notChecked 14→13, 3→2, 14→13), byDesign
untouched. 170 tests. `--refresh`: register 21 = forge 21.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CTNGvxzCLZp3UXfibYG4kb

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "repo-standard",
-  "version": "0.8.1",
+  "version": "0.9.0",
   "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"