fix: v2.3.1 — correct version, say why a plugin update failed, gitignored files in Files

- v2.3.0's tree reported 2.2.1, so every install saw an update forever;
  package.json, the lockfile, openapi.yaml, the CLAUDE.md marker and the
  snapshot now read 2.3.1
- A failed plugin-update step records the tail of the command's stdout and
  stderr plus its exit code or signal (failureText); plugin-bootstrap.js
  prints its refusal on stdout, which the verdict used to drop. Update all
  uses the same text
- updates.test.js never applies an update: it skips when the checkout is
  behind a release (apply ran npm run setup and pruned dev dependencies)
- Files tree lists gitignored files and folders, named in orange
  (addIgnored in git-diff.js); change-tree rows indent in whole steps

client/src/pages/__tests__/__snapshots__/screens.snapshot.test.tsx.snap

@@ -6913,7 +6913,7 @@ exports[`screen snapshots > Settings — about 1`] = `
             <p
               class="text-[10px] text-status-warning/90 mt-1"
             >
-              UI build v2.2.1 (rebuild client to match)
+              UI build v2.3.1 (rebuild client to match)
             </p>
           </div>
           <div