feat(chronik): add ADR-003 + Paraglide keys for /chronik page (de/en/es)

- docs/adr/003-chronik-unified-activity-feed.md: records the session-rollup
  decision (LAG + 120-min gap), the dedupe deletion, the single-endpoint
  composition, and the German-URL convention.
- frontend/messages/{de,en,es}.json: adds chronik_* keys for page title,
  Für-dich box, filter pills, day headers, singleton/rollup verb variants
  per kind, empty states, error card, Mehr-laden pagination, and the Bell
  footer link retarget.

No pluralization via ICU match — separate singleton/rollup keys per verb,
per the Felix discussion (comment #3573).

Part of #285.

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

frontend/messages/es.json

@@ -751,5 +751,44 @@
 	"audit_action_comment_added": "comentó:",
 	"audit_action_mention_created": "te mencionó en",
 
-	"dropzone_release": "Suelta para subir"
+	"dropzone_release": "Suelta para subir",
+
+	"chronik_page_title": "Crónica",
+	"chronik_for_you_caption": "Para ti",
+	"chronik_for_you_count": "{count} nuevas",
+	"chronik_mark_read_aria": "Marcar como leído",
+	"chronik_mark_all_read": "Marcar todas leídas",
+	"chronik_inbox_zero_title": "Sin nuevas menciones",
+	"chronik_inbox_zero_link": "Ver menciones anteriores →",
+	"chronik_filter_label": "Filtrar actividad",
+	"chronik_filter_all": "Todas",
+	"chronik_filter_for_you": "Para ti",
+	"chronik_filter_uploaded": "Subidos",
+	"chronik_filter_transcription": "Transcripción",
+	"chronik_filter_comments": "Comentarios",
+	"chronik_day_today": "Hoy",
+	"chronik_day_yesterday": "Ayer",
+	"chronik_day_this_week": "Esta semana",
+	"chronik_day_older": "Anterior",
+	"chronik_singleton_text_saved": "{actor} transcribió un bloque en {doc}",
+	"chronik_rollup_text_saved": "{actor} transcribió {count} bloques en {doc}",
+	"chronik_singleton_uploaded": "{actor} subió {doc}",
+	"chronik_rollup_uploaded": "{actor} subió {count} documentos",
+	"chronik_singleton_reviewed": "{actor} revisó un bloque en {doc}",
+	"chronik_rollup_reviewed": "{actor} revisó {count} bloques en {doc}",
+	"chronik_singleton_annotated": "{actor} anotó {doc}",
+	"chronik_rollup_annotated": "{actor} anotó {doc} {count}×",
+	"chronik_comment_added": "{actor} comentó en {doc}",
+	"chronik_mention_created": "{actor} te mencionó en {doc}",
+	"chronik_reply_received": "{actor} te respondió en {doc}",
+	"chronik_empty_first_run_title": "Aún no ha pasado nada",
+	"chronik_empty_first_run_body": "En cuanto alguien de la familia suba o transcriba un documento, la actividad aparecerá aquí.",
+	"chronik_empty_filter_title": "Nada en esta vista",
+	"chronik_empty_filter_body": "No hay entradas para este filtro.",
+	"chronik_error_title": "No se pudo cargar la crónica.",
+	"chronik_error_retry": "Reintentar",
+	"chronik_load_more": "Cargar más",
+	"chronik_loading": "Cargando …",
+	"chronik_load_more_announcement": "{count} entradas más cargadas",
+	"chronik_view_all": "Abrir crónica →"
 }