feat(transcription): show block numbers on PDF annotation overlays

Add blockNumbers prop through AnnotationLayer → PdfViewer → DocumentViewer.
Each turquoise annotation rectangle now shows a numbered badge (top-left,
matching the block card number in the right panel).

Block numbers are derived from sorted transcriptionBlocks, mapped by
annotationId, creating a visual link between PDF regions and block cards.

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

frontend/src/lib/components/AnnotationLayer.svelte

@@ -12,12 +12,14 @@ let {
 	annotations = [],
 	canDraw,
 	color,
+	blockNumbers = {},
 	onDraw,
 	onAnnotationClick
 }: {
 	annotations: Annotation[];
 	canDraw: boolean;
 	color: string;
+	blockNumbers?: Record<string, number>;
 	onDraw: (rect: DrawRect) => void;
 	onAnnotationClick?: (id: string) => void;
 } = $props();
@@ -125,7 +127,32 @@ const containerStyle = $derived(
 				cursor: pointer;
 				transition: background-color 0.15s ease, box-shadow 0.15s ease;
 			"
-		></div>
+		>
+			{#if blockNumbers[annotation.id]}
+				<div
+					style="
+						position: absolute;
+						top: -8px;
+						left: -8px;
+						width: 20px;
+						height: 20px;
+						border-radius: 50%;
+						background-color: {annotation.color};
+						color: white;
+						font-size: 11px;
+						font-family: sans-serif;
+						font-weight: 700;
+						display: flex;
+						align-items: center;
+						justify-content: center;
+						pointer-events: none;
+						box-shadow: 0 1px 3px rgba(0,0,0,0.3);
+					"
+				>
+					{blockNumbers[annotation.id]}
+				</div>
+			{/if}
+		</div>
 	{/each}
 
 	{#if drawRect && drawRect.width > 0}

frontend/src/lib/components/DocumentViewer.svelte

@@ -17,6 +17,7 @@ type Props = {
 	isLoading: boolean;
 	error: string;
 	transcribeMode?: boolean;
+	blockNumbers?: Record<string, number>;
 	activeAnnotationId: string | null;
 	onAnnotationClick: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
@@ -28,6 +29,7 @@ let {
 	isLoading,
 	error,
 	transcribeMode = false,
+	blockNumbers = {},
 	activeAnnotationId = $bindable(),
 	onAnnotationClick,
 	onTranscriptionDraw
@@ -83,6 +85,7 @@ let {
 			url={fileUrl}
 			documentId={doc.id}
 			transcribeMode={transcribeMode}
+			blockNumbers={blockNumbers}
 			bind:activeAnnotationId={activeAnnotationId}
 			onAnnotationClick={onAnnotationClick}
 			onTranscriptionDraw={onTranscriptionDraw}

frontend/src/lib/components/PdfViewer.svelte

@@ -11,6 +11,7 @@ let {
 	url,
 	documentId = '',
 	transcribeMode = false,
+	blockNumbers = {},
 	activeAnnotationId = $bindable<string | null>(null),
 	onAnnotationClick,
 	onTranscriptionDraw,
@@ -19,6 +20,7 @@ let {
 	url: string;
 	documentId?: string;
 	transcribeMode?: boolean;
+	blockNumbers?: Record<string, number>;
 	activeAnnotationId?: string | null;
 	onAnnotationClick?: (id: string) => void;
 	onTranscriptionDraw?: (rect: DrawRect) => void;
@@ -424,6 +426,7 @@ function zoomOut() {
 								annotations={visibleAnnotations.filter((a) => a.pageNumber === currentPage)}
 								canDraw={transcribeMode}
 								color={TRANSCRIPTION_COLOR}
+								blockNumbers={blockNumbers}
 								onDraw={handleDraw}
 								onAnnotationClick={handleAnnotationClick}
 							/>

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

@@ -55,6 +55,14 @@ let activeAnnotationId = $state<string | null>(null);
 
 let transcriptionBlocks = $state<TranscriptionBlockData[]>([]);
 
+const blockNumbers = $derived(
+	Object.fromEntries(
+		[...transcriptionBlocks]
+			.sort((a, b) => a.sortOrder - b.sortOrder)
+			.map((b, i) => [b.annotationId, i + 1])
+	)
+);
+
 async function loadTranscriptionBlocks() {
 	if (!doc?.id) return;
 	try {
@@ -197,6 +205,7 @@ onMount(() => {
 				isLoading={isLoading}
 				error={fileError}
 				transcribeMode={transcribeMode}
+				blockNumbers={blockNumbers}
 				bind:activeAnnotationId={activeAnnotationId}
 				onAnnotationClick={handleAnnotationClick}
 				onTranscriptionDraw={createBlockFromDraw}