refactor(profile): visual voice picker, playback toggles, danger zone

- Replace voice <select> with a two-column card grid grouped by engine
  (Kokoro GPU / Pocket TTS CPU / Cloudflare AI); each card has a per-voice
  sample play/pause button matching AudioPlayer behaviour
- Add Announce chapter and Audio mode (Stream/Generate) toggles to a
  unified Playback row in Preferences; Audio mode toggle disabled for
  CF AI voices
- Remove duplicate PUT /api/settings from the profile page; all writes
  go directly into audioStore / theme context and the layout's single
  debounced effect persists them
- Add Danger Zone section: collapsible, requires typing username to
  unlock Delete account button; calls DELETE /api/profile
- Add deleteUserAccount() to pocketbase.ts: purges user_settings,
  user_library, progress, comment_votes, book_ratings,
  user_subscriptions, notifications, user_sessions then the
  app_users record
- Add DELETE /api/profile server route (auth-guarded)

ui/src/lib/server/pocketbase.ts

@@ -1415,6 +1415,56 @@ export async function revokeAllUserSessions(userId: string): Promise<void> {
 	);
 }
 
+/**
+ * Delete all data associated with a user account:
+ *   - user_settings, user_library, progress, comment_votes, book_ratings,
+ *     user_subscriptions, user_sessions, notifications rows owned by the user
+ *   - the app_users record itself
+ *
+ * Does NOT delete audio files from MinIO (shared cache) or book comments
+ * (anonymised to preserve discussion threads).
+ */
+export async function deleteUserAccount(userId: string, sessionId: string): Promise<void> {
+	const collections = [
+		{ name: 'user_settings',      filter: `(user_id="${userId}" || session_id="${sessionId}")` },
+		{ name: 'user_library',       filter: `(user_id="${userId}" || session_id="${sessionId}")` },
+		{ name: 'progress',           filter: `(user_id="${userId}" || session_id="${sessionId}")` },
+		{ name: 'comment_votes',      filter: `user_id="${userId}"` },
+		{ name: 'book_ratings',       filter: `user_id="${userId}"` },
+		{ name: 'user_subscriptions', filter: `(follower_id="${userId}" || followee_id="${userId}")` },
+		{ name: 'notifications',      filter: `user_id="${userId}"` },
+		{ name: 'user_sessions',      filter: `user_id="${userId}"` },
+	];
+
+	const token = await getToken();
+
+	for (const { name, filter } of collections) {
+		try {
+			const rows = await listAll<{ id: string }>(name, filter);
+			await Promise.all(
+				rows.map((r) =>
+					fetch(`${PB_URL}/api/collections/${name}/records/${r.id}`, {
+						method: 'DELETE',
+						headers: { Authorization: `Bearer ${token}` }
+					}).catch(() => {})
+				)
+			);
+		} catch {
+			// Best-effort: log and continue so one failure doesn't abort the rest
+			log.warn('pocketbase', `deleteUserAccount: failed to purge ${name}`, { userId });
+		}
+	}
+
+	// Delete the user record last
+	const res = await pbDelete(`/api/collections/app_users/records/${userId}`);
+	if (!res.ok) {
+		const body = await res.text().catch(() => '');
+		log.error('pocketbase', 'deleteUserAccount: failed to delete app_users record', { userId, status: res.status, body });
+		throw new Error(`Failed to delete user record (${res.status})`);
+	}
+	log.info('pocketbase', 'deleteUserAccount: account deleted', { userId });
+}
+
 /**
  * Update the avatar_url field for a user record.
  */