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/lib/types.ts

@@ -2764,6 +2764,8 @@ export interface LaneTreeEntry {
   status?: string;
   /** A folder with a changed or untracked file anywhere under it. */
   changed?: true;
+  /** Ignored by git (`.gitignore`) — drawn orange in the Files tree. */
+  ignored?: true;
 }
 
 /** One row of a rendered diff — both gutters already resolved server-side. */