ui(settings): restructure Normalization section for clarity and breathing room

The mode picker (Off / ReplayGain / LUFS) used to live in the right-hand
action slot of a settings-toggle-row and the per-mode controls were
stacked into the same parent with footer-style help text. Hard to scan,
visually cramped, and odd compared to the rest of the Settings page.

Refactor:

- Mode picker becomes a full-width segmented row with even-flex buttons,
  using the new .settings-segmented utility.
- Each mode renders its own .settings-norm-block sub-section with a
  subtle accent tint and border so the active configuration reads as
  one coherent group.
- Inside the block, every setting is its own .settings-norm-field
  (control row + per-control help text immediately below). 1.1 rem gap
  between fields, 0.45 rem between row and help — clearly groups
  related text without crowding.
- Sliders no longer max-cap at 200 px and instead flex to fill the row.
- Inactive ghost buttons (Off, ReplayGain, RG mode, LUFS targets) get a
  visible border and a faint surface tint so they read as selectable
  slots in dark themes too.
- LUFS mode gets a dedicated note-box explaining that brief volume drift
  on the very first play of a new track is the analysis pass at work,
  not a bug — subsequent plays use the cached measurement, and queued
  tracks are usually pre-analysed during the previous song.
- "Trim before measurement (dB)" renamed to "Pre-analysis attenuation"
  (and equivalents in 8 locales).
- New i18n keys: normalizationDesc, normalizationOff/ReplayGain/Lufs,
  loudnessTargetLufsDesc, loudnessFirstPlayNote, replayGainPreGainDesc,
  replayGainFallbackDesc.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/es.ts

@@ -839,13 +839,22 @@ export const esTranslation = {
     replayGainTrack: 'Pista',
     replayGainAlbum: 'Álbum',
     replayGainPreGain: 'Pre-Ganancia (archivos etiquetados)',
+    replayGainPreGainDesc: 'Aumento universal añadido a cada cálculo de ReplayGain. Útil si tu biblioteca te parece globalmente demasiado baja.',
     replayGainFallback: 'Respaldo (sin etiquetar / radio)',
+    replayGainFallbackDesc: 'Se aplica a pistas (y emisoras de radio) sin etiquetas ReplayGain, para que el contenido sin etiquetar no salte más fuerte que el resto.',
     normalization: 'Normalización',
+    normalizationDesc: 'Iguala el volumen percibido entre pistas, álbumes y radio.',
+    normalizationOff: 'Apagado',
+    normalizationReplayGain: 'ReplayGain',
+    normalizationLufs: 'LUFS',
     loudnessTargetLufs: 'LUFS objetivo',
-    loudnessPreAnalysisAttenuation: 'Atenuación antes de medir (dB)',
+    loudnessTargetLufsDesc: 'Volumen de referencia al que se ajustan todas las pistas. Valor más bajo = salida más fuerte. Los servicios de streaming suelen rondar los -14 LUFS.',
+    loudnessPreAnalysisAttenuation: 'Atenuación antes de medir',
     loudnessPreAnalysisAttenuationDesc:
       'Atenúa hasta que la loudness del tema esté guardada. En streaming luego solo hay estimaciones aproximadas. 0 dB = ninguna; más negativo = más bajo.',
     loudnessPreAnalysisAttenuationReset: 'Predeterminado',
+    loudnessFirstPlayNote:
+      'En la primera reproducción de un tema nuevo el volumen puede oscilar brevemente mientras se mide. La siguiente vez se usa la medición guardada y todo permanece estable. Las pistas próximas en la cola suelen analizarse durante la canción anterior, por lo que en la práctica esto rara vez ocurre.',
     crossfade: 'Crossfade',
     crossfadeDesc: 'Transición entre pistas',
     crossfadeSecs: '{{n}} s',