feat(playback): stream buffering UI, M4A moov-at-end streaming, hot-cache spill (#737)

* feat(playback): stream buffering UI, ranged M4A tail prefetch, demuxer fix

Defer seekbar/progress until HTTP stream is armed for both legacy and
RangedHttpSource; show buffering overlay on cover art. Add MP4 tail
prefetch and Symphonia isomp4 bounded-mdat/moov-at-EOF probing so
moov-at-end M4A can start without reading the full mdat.

* feat(hot-cache): spill large ranged streams to disk for promote

When a ranged HTTP download completes above the 64 MiB RAM promote cap,
write the existing buffer once to app-data stream-spill/ and register it
for hot-cache promote (rename) and replay via fetch_data. Analysis seeds
from the spill file up to the local-file cap (512 MiB).

* fix(ui): stream buffering — grayscale cover and static clock icon

Desaturate player and queue cover art while isPlaybackBuffering; keep a
non-animated clock overlay for visibility without the spinning animation.

* fix(playback): review follow-up — tests, i18n, spill cleanup, changelog

Clippy and test layout fixes; stream spill orphan cleanup on startup;
buffering flag guard in progress handler; bufferingStream in all player
locales; CHANGELOG and contributor credits for stream/M4A work.

* docs: attribute stream buffering and M4A streaming to PR #737

* test(audio): avoid create_engine in stream spill unit test

CI runners have no audio output device; test spill take/consume via
the Mutex slot only, matching install_stream_completed_spill tests.

src/locales/de/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Vorheriger Titel',
   play: 'Play',
   pause: 'Pause',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Vorschau läuft',
   previewLabel: 'Vorschau',
   delayModalTitle: 'Timer',

src/locales/en/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Previous Track',
   play: 'Play',
   pause: 'Pause',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Preview playing',
   previewLabel: 'Preview',
   delayModalTitle: 'Timer',

src/locales/es/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Pista Anterior',
   play: 'Reproducir',
   pause: 'Pausa',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Vista previa activa',
   previewLabel: 'Vista previa',
   delayModalTitle: 'Temporizador',

src/locales/fr/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Piste précédente',
   play: 'Lecture',
   pause: 'Pause',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Aperçu en cours',
   previewLabel: 'Aperçu',
   delayModalTitle: 'Minuteur',

src/locales/nb/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Forrige spor',
   play: 'Spill av',
   pause: 'Pause',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Forhåndsvisning spilles av',
   previewLabel: 'Forhåndsvisning',
   delayModalTitle: 'Tidsur',

src/locales/nl/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Vorig nummer',
   play: 'Afspelen',
   pause: 'Pauzeren',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Voorbeeld speelt af',
   previewLabel: 'Voorbeeld',
   delayModalTitle: 'Timer',

src/locales/ro/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Piesa anterioară',
   play: 'Redă',
   pause: 'Pauză',
+  bufferingStream: 'Loading track from server',
   previewActive: 'Previzualizează redarea',
   previewLabel: 'Previzualizare',
   delayModalTitle: 'Temporizator',

src/locales/ru/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: 'Предыдущий трек',
   play: 'Играть',
   pause: 'Пауза',
+  bufferingStream: 'Загрузка трека с сервера',
   previewActive: 'Превью воспроизводится',
   previewLabel: 'Превью',
   delayModalTitle: 'Таймер',

src/locales/zh/player.ts

@@ -9,6 +9,7 @@ export const player = {
   prev: '上一首',
   play: '播放',
   pause: '暂停',
+  bufferingStream: 'Loading track from server',
   previewActive: '正在试听',
   previewLabel: '试听',
   delayModalTitle: '定时',