feat(ui): add CorrespondenzHero with discovery headline and large typeahead

New centred hero component for the Briefwechsel page: headline
"Wessen Briefe möchten Sie lesen?", cross-link to document search,
h-14 PersonTypeahead, and recent persons chips. Adds `large` prop
to PersonTypeahead and `conv_hero_crosslink` message key.

Refs: #179

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/de.json

@@ -141,6 +141,7 @@
 	"conv_sort_oldest": "Älteste zuerst",
 	"conv_empty_heading": "Wessen Briefe möchten Sie lesen?",
 	"conv_empty_text": "Wähle eine Person aus dem Archiv um deren Briefe zu sehen — mit oder ohne Korrespondent.",
+	"conv_hero_crosslink": "Suchen Sie ein bestimmtes Dokument? → Zur Dokumentensuche",
 	"conv_no_results_heading": "Keine Dokumente gefunden.",
 	"conv_no_results_text": "Versuchen Sie, den Zeitraum anzupassen.",
 	"conv_swap_btn": "Personen tauschen",

frontend/messages/en.json

@@ -141,6 +141,7 @@
 	"conv_sort_oldest": "Oldest first",
 	"conv_empty_heading": "Whose letters would you like to read?",
 	"conv_empty_text": "Choose a person from the archive to see their letters — with or without a correspondent.",
+	"conv_hero_crosslink": "Looking for a specific document? → Go to document search",
 	"conv_no_results_heading": "No documents found.",
 	"conv_no_results_text": "Try adjusting the time period.",
 	"conv_swap_btn": "Swap persons",

frontend/messages/es.json

@@ -141,6 +141,7 @@
 	"conv_sort_oldest": "Más antiguo primero",
 	"conv_empty_heading": "¿De quién desea leer las cartas?",
 	"conv_empty_text": "Elige una persona del archivo para ver sus cartas — con o sin corresponsal.",
+	"conv_hero_crosslink": "¿Busca un documento en particular? → Ir a la búsqueda",
 	"conv_no_results_heading": "No se encontraron documentos.",
 	"conv_no_results_text": "Intente ajustar el período de tiempo.",
 	"conv_swap_btn": "Intercambiar personas",