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.ts

@@ -0,0 +1,51 @@
+/** Step log of the unattended end-to-end self-test: one entry per step with its verdict and timing. */
+
+export interface StepResult {
+  name: string;
+  ok: boolean;
+  ms: number;
+  detail: string;
+}
+
+export interface StepLog {
+  steps: StepResult[];
+  /**
+   * Runs one step. The body returns its detail text, or throws to fail. A body may also return
+   * `{ ok: false, detail }` for a failed expectation. Never throws; resolves to the recorded result.
+   */
+  run(name: string, body: () => Promise<string | { ok: boolean; detail: string }>): Promise<StepResult>;
+}
+
+const errText = (e: unknown) => (e instanceof Error ? `${e.name}: ${e.message}` : String(e));
+
+export function createStepLog(now: () => number = () => performance.now()): StepLog {
+  const steps: StepResult[] = [];
+  return {
+    steps,
+    async run(name, body) {
+      const t0 = now();
+      let result: StepResult;
+      try {
+        const r = await body();
+        const { ok, detail } = typeof r === "string" ? { ok: true, detail: r } : r;
+        result = { name, ok, ms: Math.round(now() - t0), detail };
+      } catch (e) {
+        result = { name, ok: false, ms: Math.round(now() - t0), detail: errText(e) };
+      }
+      steps.push(result);
+      return result;
+    },
+  };
+}
+
+/** The directory part of an absolute path, whichever separator it uses. */
+export function dirOf(path: string): string {
+  const i = Math.max(path.lastIndexOf("/"), path.lastIndexOf("\\"));
+  return i <= 0 ? path.slice(0, i + 1) : path.slice(0, i);
+}
+
+export function bytesEqual(a: Uint8Array, b: Uint8Array): boolean {
+  if (a.byteLength !== b.byteLength) return false;
+  for (let i = 0; i < a.byteLength; i++) if (a[i] !== b[i]) return false;
+  return true;
+}