feat(frontend): rename route to /korrespondenz, update i18n, regen API types

Moves conversations/ to korrespondenz/, updates all internal links,
renames nav label and page heading to Korrespondenz across de/en/es,
and adds all new i18n keys for the redesigned strip and log.

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

frontend/src/lib/components/PanelMetadata.svelte

@@ -175,7 +175,7 @@ let { doc }: { doc: Doc } = $props();
 
 							{#if doc.sender}
 								<a
-									href="/conversations?senderId={doc.sender.id}&receiverId={receiver.id}"
+									href="/korrespondenz?senderId={doc.sender.id}&receiverId={receiver.id}"
 									class="text-ink-3 transition hover:text-accent"
 									title={m.doc_conversation_title()}
 								>