feat(ui): add collapsible PDF strip and abbreviated labels on mobile

PDF viewer collapses to 70px on mobile in read mode, expandable to
50vh. Toggle button with chevron. Paragraph tap auto-expands strip.
Mode toggle abbreviates to "Bearb." on small screens.

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

frontend/src/lib/components/TranscriptionPanelHeader.svelte

@@ -54,12 +54,13 @@ function handleReadClick() {
 				? 'bg-primary text-primary-fg'
 				: 'text-ink-2 hover:text-ink'}"
 		>
-			{m.mode_edit()}
+			<span class="md:hidden">{m.mode_edit_short()}</span>
+			<span class="hidden md:inline">{m.mode_edit()}</span>
 		</button>
 	</div>
 
-	<!-- Status line -->
-	<p class="text-xs text-ink-2">
+	<!-- Status line (hidden on mobile to save space) -->
+	<p class="hidden text-xs text-ink-2 md:block">
 		{#if blockCount === 1}
 			{m.transcription_status_section()}
 		{:else}

frontend/src/routes/documents/[id]/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 import { onMount } from 'svelte';
+import { m } from '$lib/paraglide/messages.js';
 import DocumentTopBar from '$lib/components/DocumentTopBar.svelte';
 import DocumentViewer from '$lib/components/DocumentViewer.svelte';
 import TranscriptionEditView from '$lib/components/TranscriptionEditView.svelte';
@@ -55,6 +56,7 @@ let panelMode = $state<'read' | 'edit'>('read');
 let activeAnnotationId = $state<string | null>(null);
 let highlightBlockId = $state<string | null>(null);
 let flashAnnotationId = $state<string | null>(null);
+let pdfStripExpanded = $state(false);
 
 const prefersReducedMotion = $derived(
 	typeof window !== 'undefined' && window.matchMedia('(prefers-reduced-motion: reduce)').matches
@@ -187,6 +189,7 @@ async function handleAnnotationClick(annotationId: string) {
 function handleParagraphClick(annotationId: string) {
 	activeAnnotationId = annotationId;
 	flashAnnotationId = annotationId;
+	pdfStripExpanded = true;
 	setTimeout(
 		() => {
 			flashAnnotationId = null;
@@ -246,7 +249,9 @@ onMount(() => {
 
 	<div class="relative flex-1 overflow-hidden {transcribeMode ? 'flex flex-col md:flex-row' : ''}">
 		<div
-			class={transcribeMode ? 'relative min-h-[40vh] flex-1 overflow-hidden md:min-h-0' : 'absolute inset-0'}
+			class={transcribeMode
+				? `relative flex-1 overflow-hidden md:min-h-0 ${panelMode === 'read' ? (pdfStripExpanded ? 'max-h-[50vh] min-h-[50vh] md:max-h-none md:min-h-0' : 'max-h-[70px] min-h-[70px] md:max-h-none md:min-h-0') : 'min-h-[40vh]'} transition-[min-height,max-height] duration-300`
+				: 'absolute inset-0'}
 		>
 			<DocumentViewer
 				doc={doc}
@@ -264,9 +269,30 @@ onMount(() => {
 			/>
 		</div>
 
+		{#if transcribeMode && panelMode === 'read'}
+			<button
+				type="button"
+				onclick={() => (pdfStripExpanded = !pdfStripExpanded)}
+				class="flex h-7 w-full shrink-0 items-center justify-center border-t border-line bg-muted text-xs font-semibold text-ink-2 md:hidden"
+				aria-label={pdfStripExpanded ? m.scan_collapse() : m.scan_expand()}
+			>
+				<svg
+					class="mr-1 h-3 w-3 transition-transform duration-200 {pdfStripExpanded ? 'rotate-180' : ''}"
+					viewBox="0 0 24 24"
+					fill="none"
+					stroke="currentColor"
+					stroke-width="2.5"
+					aria-hidden="true"
+				>
+					<path stroke-linecap="round" stroke-linejoin="round" d="M19 9l-7 7-7-7" />
+				</svg>
+				{pdfStripExpanded ? m.scan_collapse() : m.scan_expand()}
+			</button>
+		{/if}
+
 		{#if transcribeMode}
 			<div
-				class="flex shrink-0 flex-col border-t border-line md:w-[400px] md:border-t-0 md:border-l lg:w-[480px]"
+				class="flex min-h-0 flex-1 shrink-0 flex-col border-t border-line md:w-[400px] md:flex-none md:border-t-0 md:border-l lg:w-[480px]"
 			>
 				<TranscriptionPanelHeader
 					mode={panelMode}