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/schemas.ts

@@ -261,6 +261,60 @@ export type HomeworkMakeRecord = Extract<HomeworkRecord, { mode: "make" }>;
 export type HomeworkGuideRecord = Extract<HomeworkRecord, { mode: "guide" }>;
 export type HomeworkCheckRecord = Extract<HomeworkRecord, { mode: "check" }>;
 
+/* ------------------------------------------------------------------ */
+/* Podcasts (notes turned into a spoken episode)                       */
+/* ------------------------------------------------------------------ */
+
+export type PodcastSection = { heading: string; text: string };
+
+/** As produced by the model (no id yet). */
+export const generatedPodcastSchema = z.object({
+  title: z.string().min(1).max(200),
+  language: z.string().max(60).optional(),
+  summary: z.string().max(400).optional(),
+  sections: z
+    .array(
+      z.object({
+        heading: z.string().min(1).max(120),
+        text: z.string().min(1).max(4000),
+      }),
+    )
+    .min(1)
+    .max(12),
+});
+export type GeneratedPodcast = z.infer<typeof generatedPodcastSchema>;
+
+/** Stored episode: the script plus where it came from and where the listener
+ *  got to (so reopening it resumes, Spotify-style). */
+export type Podcast = {
+  id: string;
+  title: string;
+  summary?: string;
+  language?: string;
+  sourceText: string;
+  createdAt: number;
+  updatedAt: number;
+  sections: PodcastSection[];
+  progress?: { section: number; word: number; at: number };
+};
+
+export const podcastSchema: z.ZodType<Podcast> = z.object({
+  id: z.string().min(1).max(80),
+  title: z.string().min(1).max(200),
+  summary: z.string().max(400).optional(),
+  language: z.string().max(60).optional(),
+  sourceText: z.string().max(40_000),
+  createdAt: z.number(),
+  updatedAt: z.number(),
+  sections: z
+    .array(z.object({ heading: z.string().min(1).max(120), text: z.string().min(1).max(4000) }))
+    .min(1)
+    .max(12),
+  progress: z
+    .object({ section: z.number().int().min(0), word: z.number().int().min(0), at: z.number() })
+    .optional(),
+});
+
 /* ------------------------------------------------------------------ */
 /* Client-side deck types (activity + id/xp, plus storage metadata)     */
 /* ------------------------------------------------------------------ */