fix(ui): update Spanish translations and add missing gain keys (#5433)

* fix(ui): update Spanish translations and add missing gain keys

- Add missing 'albumGain' and 'trackGain' keys (matches recent additions in pt-br, ru)
- Translate 'Playlists' and 'Shared Playlists' to 'Listas de reproducción' / '...compartidas'
- Translate 'OFFLINE' (server down indicator) to 'DESCONECTADO'

Spanish translation now covers 553/553 keys (was 551/553).

Signed-off-by: Daniel Banariba <banaribad@gmail.com>

* fix(ui): address review feedback on Spanish translations

- Use 'Ganancia del álbum' (with article 'del') for consistency with the existing pattern in line 624 ('album': 'Ganancia del álbum') and 'Artista del álbum'. Thanks @gemini-code-assist for the catch.
- Revert 'playlists' and 'sharedPlaylists' to keep the loanword 'Playlist(s)' which is the form actually used by Spanish-speaking music app users (Spotify ES, etc.) and matches existing usage elsewhere in this same file (e.g. line 48 'Agregar a la playlist').

Signed-off-by: Daniel Banariba <banaribad@gmail.com>

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Signed-off-by: Daniel Banariba <banaribad@gmail.com>
Co-authored-by: Deluan Quintão <deluan@navidrome.org>

resources/i18n/es.json

@@ -35,6 +35,8 @@
         "rawTags": "Etiquetas sin procesar",
         "bitDepth": "Profundidad de bits",
         "sampleRate": "Frecuencia de muestreo",
+        "albumGain": "Ganancia del álbum",
+        "trackGain": "Ganancia de pista",
         "missing": "Faltante",
         "libraryName": "Biblioteca",
         "composer": "Compositor",
@@ -693,7 +695,7 @@
     "quickScan": "Escaneo rápido",
     "fullScan": "Escaneo completo",
     "serverUptime": "Uptime del servidor",
-    "serverDown": "OFFLINE",
+    "serverDown": "DESCONECTADO",
     "scanType": "Tipo",
     "status": "Error de escaneo",
     "elapsedTime": "Tiempo transcurrido",