feat(i18n): extract hardcoded strings in DocumentEditLayout to i18n keys

Adds label_required_fields to all three locales. Fixes "Datei ersetzen"
toolbar colors to use semantic ink tokens (readable in both light and dark
pdf-bg themes).

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

frontend/messages/de.json

@@ -53,6 +53,7 @@
 	"form_placeholder_archive_location": "z.B. Schrank 3, Mappe B",
 	"form_helper_archive_location": "Wo befindet sich das Originaldokument?",
 	"label_optional": "Optional",
+	"label_required_fields": "Pflichtfelder",
 	"login_heading": "Anmelden",
 	"login_label_username": "Benutzername",
 	"login_label_password": "Passwort",

frontend/messages/en.json

@@ -53,6 +53,7 @@
 	"form_placeholder_archive_location": "e.g. Cabinet 3, Folder B",
 	"form_helper_archive_location": "Where is the original document stored?",
 	"label_optional": "Optional",
+	"label_required_fields": "Required fields",
 	"login_heading": "Sign in",
 	"login_label_username": "Username",
 	"login_label_password": "Password",

frontend/messages/es.json

@@ -53,6 +53,7 @@
 	"form_placeholder_archive_location": "p.ej. Armario 3, Carpeta B",
 	"form_helper_archive_location": "¿Dónde se encuentra el documento original?",
 	"label_optional": "Opcional",
+	"label_required_fields": "Campos obligatorios",
 	"login_heading": "Iniciar sesión",
 	"login_label_username": "Usuario",
 	"login_label_password": "Contraseña",

frontend/src/lib/components/document/DocumentEditLayout.svelte

@@ -125,14 +125,16 @@ async function handleReplaceFile(e: Event) {
 
 	<!-- Required-fields progress bar -->
 	<div class="flex items-center gap-3 border-b border-line bg-surface px-6 py-1.5">
-		<span class="text-xs font-bold tracking-widest text-ink-3 uppercase">Pflichtfelder</span>
+		<span class="text-xs font-bold tracking-widest text-ink-3 uppercase"
+			>{m.label_required_fields()}</span
+		>
 		<div
 			class="h-0.5 flex-1 rounded-full bg-line"
 			role="progressbar"
 			aria-valuenow={requiredFilled}
 			aria-valuemin={0}
 			aria-valuemax={3}
-			aria-label="Pflichtfelder"
+			aria-label={m.label_required_fields()}
 		>
 			<div
 				class="h-full rounded-full bg-brand-navy transition-all duration-300"
@@ -157,11 +159,11 @@ async function handleReplaceFile(e: Event) {
 				/>
 			{:else}
 				<!-- Datei ersetzen toolbar -->
-				<div class="flex shrink-0 items-center border-b border-white/10 bg-pdf-bg px-4 py-1.5">
+				<div class="flex shrink-0 items-center border-b border-line bg-surface px-4 py-1.5">
 					<label
-						class="ml-auto flex min-h-[44px] cursor-pointer items-center text-xs font-bold tracking-widest text-white/40 uppercase transition-colors hover:text-white/70"
+						class="ml-auto flex min-h-[44px] cursor-pointer items-center text-xs font-bold tracking-widest text-ink-3 uppercase transition-colors hover:text-ink"
 					>
-						Datei ersetzen
+						{m.doc_file_replace_label()}
 						<input type="file" class="sr-only" onchange={handleReplaceFile} />
 					</label>
 				</div>