Run browser file transcription through the long-form pipeline when asked and the VAD model is available

Adds an Advanced "Skip silence in uploaded files" option (off by default
pending measurement), the vad/longForm protocol fields, the old-path
fallback when the VAD model is missing, and a plain message for files
with no speech.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/longform-setting.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, test } from "bun:test";
+import { emptyTranscriptNotice } from "../src/lib/export";
+import {
+  LONG_FORM_DEFAULT,
+  LONG_FORM_KEY,
+  loadLongFormChoice,
+  saveLongFormChoice,
+} from "../src/lib/longForm";
+
+function memoryStorage(initial: Record<string, string> = {}) {
+  const data = { ...initial };
+  return {
+    data,
+    getItem: (key: string) => data[key] ?? null,
+    setItem: (key: string, value: string) => {
+      data[key] = value;
+    },
+  };
+}
+
+describe("long-form setting persistence (D-WS3a)", () => {
+  test("defaults when nothing is stored or storage is unavailable", () => {
+    expect(loadLongFormChoice(memoryStorage())).toBe(LONG_FORM_DEFAULT);
+    expect(loadLongFormChoice(null)).toBe(LONG_FORM_DEFAULT);
+    const throwing = {
+      getItem: () => {
+        throw new Error("denied");
+      },
+      setItem: () => {
+        throw new Error("denied");
+      },
+    };
+    expect(loadLongFormChoice(throwing)).toBe(LONG_FORM_DEFAULT);
+    expect(() => saveLongFormChoice(true, throwing)).not.toThrow();
+  });
+
+  test("round-trips an explicit choice", () => {
+    const storage = memoryStorage();
+    saveLongFormChoice(!LONG_FORM_DEFAULT, storage);
+    expect(storage.data[LONG_FORM_KEY]).toBeDefined();
+    expect(loadLongFormChoice(storage)).toBe(!LONG_FORM_DEFAULT);
+  });
+});
+
+describe("emptyTranscriptNotice (plan 001-0 Review Focus 4)", () => {
+  test("a finished transcript with no words says so plainly", () => {
+    expect(emptyTranscriptNotice({ text: "" })).toBe("No speech was found in this recording.");
+    expect(emptyTranscriptNotice({ text: "  \n" })).toBe("No speech was found in this recording.");
+  });
+
+  test("no notice while running or when there is text", () => {
+    expect(emptyTranscriptNotice(null)).toBeNull();
+    expect(emptyTranscriptNotice({ text: " Hello." })).toBeNull();
+  });
+});