fix(i18n): replace hardcoded "oder" with conv_hero_divider message key

Adds conv_hero_divider to de/en/es messages and uses it in the
CorrespondenzHero divider. Fixes i18n blocker from review.

Refs: #179

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

frontend/messages/de.json

@@ -160,6 +160,7 @@
 	"conv_suggestions_all_label": "Alle Korrespondenten von {name}",
 	"conv_letters_count": "{count} Briefe",
 	"conv_empty_search_placeholder": "Person suchen…",
+	"conv_hero_divider": "oder",
 	"conv_empty_recent_label": "Zuletzt geöffnet",
 	"conv_asym_sent": "{count} von {name} →",
 	"conv_asym_received": "{count} von {name} ←",

frontend/messages/en.json

@@ -160,6 +160,7 @@
 	"conv_suggestions_all_label": "All correspondents of {name}",
 	"conv_letters_count": "{count} letters",
 	"conv_empty_search_placeholder": "Search person…",
+	"conv_hero_divider": "or",
 	"conv_empty_recent_label": "Recently opened",
 	"conv_asym_sent": "{count} from {name} →",
 	"conv_asym_received": "{count} from {name} ←",

frontend/messages/es.json

@@ -160,6 +160,7 @@
 	"conv_suggestions_all_label": "Todos los corresponsales de {name}",
 	"conv_letters_count": "{count} cartas",
 	"conv_empty_search_placeholder": "Buscar persona…",
+	"conv_hero_divider": "o",
 	"conv_empty_recent_label": "Recientemente abiertos",
 	"conv_asym_sent": "{count} de {name} →",
 	"conv_asym_received": "{count} de {name} ←",

frontend/src/routes/briefwechsel/CorrespondenzHero.svelte

@@ -32,18 +32,18 @@ function handlePersonChange(id: string) {
 
 <div
 	data-testid="conv-hero"
-	class="mx-auto flex max-w-lg flex-col items-center gap-6 py-20 text-center"
+	class="mx-auto flex max-w-lg flex-col items-center gap-6 py-12 text-center sm:py-20"
 >
-	<!-- Cross-link to document search -->
-	<a href="/" class="text-sm text-ink-3 transition-colors hover:text-primary">
-		{m.conv_hero_crosslink()}
-	</a>
-
 	<!-- Discovery headline -->
 	<h1 class="font-serif text-2xl font-black text-ink">
 		{m.conv_empty_heading()}
 	</h1>
 
+	<!-- Cross-link to document search -->
+	<a href="/" class="text-sm text-ink-3 transition-colors hover:text-primary">
+		{m.conv_hero_crosslink()}
+	</a>
+
 	<!-- Person typeahead (large, hero-sized) -->
 	<div class="w-full max-w-sm" bind:this={typeaheadEl}>
 		<PersonTypeahead
@@ -59,7 +59,9 @@ function handlePersonChange(id: string) {
 	{#if recentPersons.length > 0}
 		<div class="flex w-full max-w-sm items-center gap-2">
 			<div class="flex-1 border-t border-line"></div>
-			<span class="text-xs font-bold tracking-wider text-ink-3 uppercase">oder</span>
+			<span class="text-xs font-bold tracking-wider text-ink-3 uppercase"
+				>{m.conv_hero_divider()}</span
+			>
 			<div class="flex-1 border-t border-line"></div>
 		</div>