feat: stream/generate audio mode toggle

Add a user-selectable playback mode stored in user_settings:
- 'stream' (default): /api/audio-stream starts playing within seconds,
  saves to MinIO concurrently — low latency
- 'generate': queue runner task, poll until full audio is ready in
  MinIO, then play via presigned URL — legacy behaviour

UI toggles in two places:
- AudioPlayer idle pill: compact '· Stream / · Generate' inline next
  to voice name and estimated duration
- ListeningMode controls row: pill alongside Auto, Announce, Sleep;
  disabled and grayed out for CF AI voices (batch-only, no streaming)

startPlayback() now branches on audioStore.audioMode for non-CF AI
voices; generate mode uses the same runner task + progress bar flow
as CF AI but without the preview clip.

PocketBase: audio_mode text field added to user_settings on
pb.libnovel.cc (live) and in pb-init-v3.sh (create block +
add_field migration line).

ui/src/lib/server/pocketbase.ts

@@ -76,6 +76,7 @@ export interface PBUserSettings {
 	font_family?: string;
 	font_size?: number;
 	announce_chapter?: boolean;
+	audio_mode?: string;
 	updated?: string;
 }
 
@@ -1013,7 +1014,7 @@ export async function getSettings(
 
 export async function saveSettings(
 	sessionId: string,
-	settings: { autoNext: boolean; voice: string; speed: number; theme?: string; locale?: string; fontFamily?: string; fontSize?: number; announceChapter?: boolean },
+	settings: { autoNext: boolean; voice: string; speed: number; theme?: string; locale?: string; fontFamily?: string; fontSize?: number; announceChapter?: boolean; audioMode?: string },
 	userId?: string
 ): Promise<void> {
 	const existing = await listOne<PBUserSettings & { id: string }>(
@@ -1033,6 +1034,7 @@ export async function saveSettings(
 	if (settings.fontFamily !== undefined) payload.font_family = settings.fontFamily;
 	if (settings.fontSize !== undefined) payload.font_size = settings.fontSize;
 	if (settings.announceChapter !== undefined) payload.announce_chapter = settings.announceChapter;
+	if (settings.audioMode !== undefined) payload.audio_mode = settings.audioMode;
 	if (userId) payload.user_id = userId;
 
 	if (existing) {