Add unattended end-to-end self-test mode for the production webview

VOICED_SELFTEST_OUT runs the Diagnostics checks plus an issue, archive,
export (searchable, flattened, re-render), cancel and archive-immutability
flow through the real IPC, writes a JSON report and exits. Inert without
the variable; doubles as the per-release gate on installed builds.

src/lib/selfTestSteps.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { bytesEqual, createStepLog, dirOf } from "./selfTestSteps";
+
+describe("createStepLog", () => {
+  it("records passes, expectation failures and throws without throwing itself", async () => {
+    let t = 0;
+    const log = createStepLog(() => (t += 10));
+    await log.run("a", async () => "fine");
+    await log.run("b", async () => ({ ok: false, detail: "wrong" }));
+    await log.run("c", async () => {
+      throw new Error("boom");
+    });
+    expect(log.steps).toEqual([
+      { name: "a", ok: true, ms: 10, detail: "fine" },
+      { name: "b", ok: false, ms: 10, detail: "wrong" },
+      { name: "c", ok: false, ms: 10, detail: "Error: boom" },
+    ]);
+  });
+});
+
+describe("dirOf / bytesEqual", () => {
+  it("splits posix and windows paths", () => {
+    expect(dirOf("/tmp/x/report.json")).toBe("/tmp/x");
+    expect(dirOf("C:\\out\\report.json")).toBe("C:\\out");
+    expect(dirOf("/report.json")).toBe("/");
+    expect(dirOf("report.json")).toBe("");
+  });
+  it("compares bytes", () => {
+    expect(bytesEqual(new Uint8Array([1, 2]), new Uint8Array([1, 2]))).toBe(true);
+    expect(bytesEqual(new Uint8Array([1, 2]), new Uint8Array([1, 3]))).toBe(false);
+    expect(bytesEqual(new Uint8Array([1]), new Uint8Array([1, 2]))).toBe(false);
+  });
+});