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

server/__tests__/plugin-update.test.js

@@ -169,3 +169,36 @@ describe("plugin-update-helper name guard", () => {
     assert.ok(!Number.isNaN(Date.parse(v.finished_at)));
   });
 });
+
+describe("plugin-update-helper failureText", () => {
+  // Required, not spawned: the helper only runs main() as a script.
+  const { failureText } = require("../../scripts/plugin-update-helper");
+
+  it("names why the bootstrap refused, which it prints on stdout", () => {
+    const err = Object.assign(new Error("Command failed: node plugin-bootstrap.js --force"), {
+      status: 1,
+      stdout: "installing…\nbootstrap: locked\n",
+      stderr: "",
+    });
+    assert.equal(failureText(err), "installing…\nbootstrap: locked\n(exit 1)");
+  });
+
+  it("keeps only the last lines, stdout then stderr", () => {
+    const err = Object.assign(new Error("x"), {
+      status: 2,
+      stdout: ["1", "2", "3", "4", "5", "6", "7"].join("\n"),
+      stderr: "boom",
+    });
+    assert.equal(failureText(err), "3\n4\n5\n6\n7\nboom\n(exit 2)");
+  });
+
+  it("says a killed command was killed, and falls back to the message when nothing was printed", () => {
+    const err = Object.assign(new Error("Command failed: node b.js --force\n"), {
+      status: null,
+      signal: "SIGTERM",
+      stdout: "",
+      stderr: "",
+    });
+    assert.equal(failureText(err), "Command failed: node b.js --force (killed by SIGTERM)");
+  });
+});