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.

lib/sync.ts

@@ -17,6 +17,7 @@ import { chatHistoryStore, ensureChatsHydrated, replaceChats } from "./chat-stor
 import { ApiError } from "./client-api";
 import { replaceFolders } from "./folders";
 import { replaceHomework } from "./homework";
+import { podcastStore, replacePodcasts } from "./podcasts";
 import { ensureLearningHydrated, learningStore, replaceLearning } from "./history";
 import { localeHeader, t } from "./i18n";
 import { authHeaders } from "./settings";
@@ -173,6 +174,7 @@ async function buildPayload(): Promise<SyncPayload> {
       decks: deckStore.getSnapshot(),
       folders: folderStore.getSnapshot(),
       homework: homeworkStore.getSnapshot(),
+      podcasts: podcastStore.getSnapshot(),
       history: learningStore.getAnswersSnapshot(),
       srs: learningStore.getSrsSnapshot(),
       chats: chatHistoryStore.getSnapshot(),
@@ -188,6 +190,7 @@ async function applyRemote(key: CryptoKey, remote: { updatedAt: number; envelope
     replaceFolders(parsed.data.folders);
     replaceDecks(parsed.data.decks);
     replaceHomework(parsed.data.homework);
+    replacePodcasts(parsed.data.podcasts ?? []);
     replaceChats(parsed.data.chats ?? []);
   });
   await replaceLearning(parsed.data.history ?? [], parsed.data.srs ?? []);