Podcast mode: notes read aloud with a lyric-style word highlight

The third segment of the note-powered wizards (Study deck / Homework /
Podcast) takes the same intake - photos, documents, pasted text, the share
target - and turns it into a spoken episode.

- prompts: PODCAST_SYSTEM_PROMPT writes for the ear (plain prose, no markdown,
  no visual references), chaptered into 3-8 sections around a length target.
- /api/podcast mirrors /api/generate's plumbing (rate limit, model gate,
  provider keys, heartbeats, the 2x deadline, the optional vision pass).
- storage: frezmo.podcasts.v1, zod-validated, included in the backup and the
  encrypted sync payload; a new library tab lists episodes with listen /
  rename / delete-with-undo, and the wizard switch deep-links in.
- player: the transcript is word-wrapped spans and the word under the voice
  rides a lyric-style highlight that keeps itself centred. Two clocks: exact
  onboundary events where the browser reports them, a per-word length timer
  where it does not (iOS Safari); the first boundary retires the timer.
  Pause = cancel + re-speak from the word, which makes resume, chapter jumps
  and tap-any-word-to-seek the same operation; the position saves on pause,
  page-hide and unmount, so reopening resumes. Speed rebuilds the engine and
  keeps playing; the Aero soundtrack pauses itself when the voice starts; a
  browser with no voice gets an honest note and a readable transcript.
- the script sits on a glass pane (plain paragraphs over Aero's grass failed
  contrast; the scan now covers the player too).

tests/podcast-test.mjs (17th suite) stubs the model and the speech engine and
drives the highlight by hand: 26 checks. All suites green, contrast clean.
Version 0.7.3, SW v95.

components/WizardModeSwitch.tsx

@@ -9,12 +9,13 @@ import { useWizardBusy } from "@/lib/wizard-busy";
 import { cn } from "@/lib/utils";
 
 /**
- * In-page switch between the two wizards (New deck ⇄ Make my homework).
- * Phones reach both through this control and the centre tab; desktop keeps
- * the rail rows as well. Hidden while either wizard is generating: leaving a
- * loading run through it would abandon the request mid-flight.
+ * In-page switch between the three note-powered wizards (New deck ⇄ Make my
+ * homework ⇄ New podcast). Phones reach the first two through this control and
+ * the centre tab; desktop keeps the rail rows as well. Hidden while a wizard
+ * is generating: leaving a loading run through it would abandon the request
+ * mid-flight.
  */
-export function WizardModeSwitch({ mode }: { mode: "deck" | "homework" }) {
+export function WizardModeSwitch({ mode }: { mode: "deck" | "homework" | "podcast" }) {
   const { t } = useI18n();
   const isPhone = useIsPhone();
   const busy = useWizardBusy();
@@ -39,6 +40,14 @@ export function WizardModeSwitch({ mode }: { mode: "deck" | "homework" }) {
         {isPhone && mode === "homework" ? <SegmentedPill layoutId="wizard-mode" /> : null}
         <span className="seg-label relative z-10">{t("wizard.mode.homework")}</span>
       </Link>
+      <Link
+        href="/podcast"
+        aria-current={mode === "podcast" ? "page" : undefined}
+        className={cn("relative", isPhone && "seg-slide")}
+      >
+        {isPhone && mode === "podcast" ? <SegmentedPill layoutId="wizard-mode" /> : null}
+        <span className="seg-label relative z-10">{t("wizard.mode.podcast")}</span>
+      </Link>
     </div>
   );
 }