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/de.ts

@@ -846,13 +846,22 @@ export const deTranslation = {
     replayGainTrack: 'Track',
     replayGainAlbum: 'Album',
     replayGainPreGain: 'Pre-Gain (getaggte Dateien)',
+    replayGainPreGainDesc: 'Pauschaler Boost, der auf jede ReplayGain-Berechnung aufaddiert wird. Hilft, wenn deine Bibliothek insgesamt zu leise wirkt.',
     replayGainFallback: 'Fallback (ohne Tags / Radio)',
+    replayGainFallbackDesc: 'Wird auf Titel (und Radio-Streams) ohne ReplayGain-Tags angewendet, damit Untagged-Inhalt nicht lauter aus dem Mix springt.',
     normalization: 'Normalisierung',
+    normalizationDesc: 'Empfundene Lautstärke über Titel, Alben und Radio angleichen.',
+    normalizationOff: 'Aus',
+    normalizationReplayGain: 'ReplayGain',
+    normalizationLufs: 'LUFS',
     loudnessTargetLufs: 'Ziel-LUFS',
-    loudnessPreAnalysisAttenuation: 'Dämpfung vor Messung (dB)',
+    loudnessTargetLufsDesc: 'Referenz-Lautstärke, an die alle Titel angepasst werden. Niedrigere Werte = lautere Ausgabe. Streaming-Dienste liegen meist bei etwa -14 LUFS.',
+    loudnessPreAnalysisAttenuation: 'Dämpfung vor Messung',
     loudnessPreAnalysisAttenuationDesc:
       'Zusätzliche Dämpfung, bis die Loudness des Titels gespeichert ist. Beim Streamen folgen nur grobe Schätzungen, keine volle Messung. 0 dB = aus; negativer = leiser.',
     loudnessPreAnalysisAttenuationReset: 'Standard',
+    loudnessFirstPlayNote:
+      'Beim ersten Abspielen eines neuen Titels kann die Lautstärke kurz schwanken, während gemessen wird. Beim nächsten Mal greift die gespeicherte Messung und alles bleibt stabil. Kommende Queue-Titel werden meist schon während des vorherigen Songs analysiert — in der Praxis tritt das daher selten auf.',
     crossfade: 'Crossfade',
     crossfadeDesc: 'Überblendung zwischen Tracks',
     crossfadeSecs: '{{n}} s',