feat(i18n): remove orphaned conversation message keys

Drop the 22 message keys that only the deleted Briefwechsel view used
(conv_* except the still-used conv_sort_newest/oldest, plus
nav_conversations, doc_conversation_title and person_correspondents_hint,
all now superseded by the retargeted card's new search keys).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/messages/de.json

@@ -26,7 +26,6 @@
 	"error_internal_error": "Ein unerwarteter Fehler ist aufgetreten.",
 	"nav_documents": "Dokumente",
 	"nav_persons": "Personen",
-	"nav_conversations": "Briefwechsel",
 	"nav_admin": "Admin",
 	"nav_logout": "Abmelden",
 	"layout_menu_open": "Menü öffnen",
@@ -189,32 +188,12 @@
 	"person_role_sender": "Gesendet",
 	"person_role_receiver": "Empfangen",
 	"person_co_correspondents_heading": "Häufige Korrespondenten",
-	"person_correspondents_hint": "klicken für Konversation",
 	"person_correspondents_search_title": "Briefe von {A} an {B} durchsuchen",
 	"person_correspondents_search_hint": "klicken, um Briefe zu durchsuchen",
 	"person_correspondents_badge_title": "Gemeinsame Briefe in beide Richtungen",
 	"person_show_more": "+ {count} weitere anzeigen",
-	"conv_label_person_a": "Person A (Absender)",
-	"conv_label_person_b": "Korrespondent",
-	"conv_label_from": "Zeitraum von",
-	"conv_label_to": "Zeitraum bis",
-	"conv_sort_label": "Sortierung:",
 	"conv_sort_newest": "Neueste zuerst",
 	"conv_sort_oldest": "Älteste zuerst",
-	"conv_empty_heading": "Wessen Briefe möchten Sie lesen?",
-	"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",
-	"conv_new_doc_link": "Neues Dokument in diesem Briefwechsel",
-	"conv_strip_sort_newest": "Neueste",
-	"conv_strip_sort_oldest": "Älteste",
-	"conv_suggestions_heading": "Häufigste Korrespondenten",
-	"conv_suggestions_all_label": "Alle Korrespondenten von {name}",
-	"conv_letters_count": "{count} Briefe",
-	"conv_hero_divider": "oder",
-	"conv_empty_recent_label": "Zuletzt geöffnet",
-	"conv_no_party": "—",
 	"dist_bar_segment": "{count} von {name}",
 	"dist_bar_aria": "Briefverteilung in diesem Zeitraum: {outCount} von {senderName}, {inCount} von {receiverName}",
 	"row_direction_sent": "Gesendet",
@@ -295,7 +274,6 @@
 	"topbar_overflow_heading": "Weitere Empfänger",
 	"topbar_overflow_show": "{count} weitere Empfänger anzeigen",
 	"doc_tag_filter_title": "Nach {name} filtern",
-	"doc_conversation_title": "Konversation anzeigen",
 	"doc_preview_iframe_title": "Dokumentvorschau",
 	"doc_image_alt": "Original-Scan",
 	"doc_no_date": "Kein Datum",