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/nb.ts

@@ -833,13 +833,22 @@ export const nbTranslation = {
     replayGainTrack: 'Spor',
     replayGainAlbum: 'Album',
     replayGainPreGain: 'Pre-Gain (taggede filer)',
+    replayGainPreGainDesc: 'Universelt løft som legges på hver ReplayGain-beregning. Nyttig hvis biblioteket ditt totalt sett virker for stille.',
     replayGainFallback: 'Reserveverdi (uten tagger / radio)',
+    replayGainFallbackDesc: 'Brukes for spor (og radiostrømmer) uten ReplayGain-tagger, slik at utagget innhold ikke spretter høyere enn resten.',
     normalization: 'Normalisering',
+    normalizationDesc: 'Jevn ut opplevd loudness mellom spor, album og radio.',
+    normalizationOff: 'Av',
+    normalizationReplayGain: 'ReplayGain',
+    normalizationLufs: 'LUFS',
     loudnessTargetLufs: 'Mål-LUFS',
-    loudnessPreAnalysisAttenuation: 'Demping før måling (dB)',
+    loudnessTargetLufsDesc: 'Referanse-loudness alle spor matches mot. Lavere tall = høyere utgang. Strømmetjenester ligger vanligvis rundt -14 LUFS.',
+    loudnessPreAnalysisAttenuation: 'Demping før måling',
     loudnessPreAnalysisAttenuationDesc:
       'Ekstra demping til loudness for sporet er lagret. Streaming bruker deretter grove anslag, ikke full måling. 0 dB = av; lavere = roligere.',
     loudnessPreAnalysisAttenuationReset: 'Standard',
+    loudnessFirstPlayNote:
+      'Første avspilling av et helt nytt spor kan drive litt i volum mens målingen skjer. Neste gang brukes den lagrede målingen, og alt blir stabilt. Kommende spor i køen blir vanligvis pre-analysert mens det forrige spilles, så dette skjer sjelden i praksis.',
     crossfade: 'Crossfade',
     crossfadeDesc: 'Tone mellom spor',
     crossfadeSecs: '{{n}}s',