i18n(transcription): add reader read-label and panel title strings (#697)

transcription_read_label ("Transkription lesen") for the read-only entry
control and transcription_panel_title ("Transkription") for the plain
header readers see instead of the Lesen/Bearbeiten toggle.

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

frontend/src/lib/document/DocumentTopBarActions.svelte

@@ -5,6 +5,7 @@ type Props = {
 	documentId: string;
 	canWrite: boolean;
 	isPdf: boolean;
+	hasTranscription: boolean;
 	transcribeMode: boolean;
 	filePath?: string | null;
 	originalFilename?: string | null;
@@ -15,17 +16,23 @@ let {
 	documentId,
 	canWrite,
 	isPdf,
+	hasTranscription,
 	transcribeMode = $bindable(),
 	filePath = null,
 	originalFilename = null,
 	fileUrl
 }: Props = $props();
+
+const canOpenTranscription = $derived((canWrite || hasTranscription) && isPdf);
+const transcriptionLabel = $derived(
+	canWrite ? m.transcription_mode_label() : m.transcription_read_label()
+);
 </script>
 
-{#if canWrite && isPdf && !transcribeMode}
+{#if canOpenTranscription && !transcribeMode}
 	<button
 		onclick={() => (transcribeMode = true)}
-		aria-label={m.transcription_mode_label()}
+		aria-label={transcriptionLabel}
 		aria-pressed={false}
 		class="hidden items-center gap-1.5 rounded border border-primary px-3 py-1.5 font-sans text-[16px] font-medium text-ink transition hover:bg-primary hover:text-primary-fg focus-visible:ring-2 focus-visible:ring-primary md:flex"
 	>
@@ -42,7 +49,7 @@ let {
 				d="M19.5 14.25v-2.625a3.375 3.375 0 00-3.375-3.375h-1.5A1.125 1.125 0 0113.5 7.125v-1.5a3.375 3.375 0 00-3.375-3.375H8.25m0 12.75h7.5m-7.5 3H12M10.5 2.25H5.625c-.621 0-1.125.504-1.125 1.125v17.25c0 .621.504 1.125 1.125 1.125h12.75c.621 0 1.125-.504 1.125-1.125V11.25a9 9 0 00-9-9z"
 			/>
 		</svg>
-		{m.transcription_mode_label()}
+		{transcriptionLabel}
 	</button>
 {/if}