refactor: move document transcription, annotation, viewer sub-packages

- transcription/: TranscriptionBlock, Column, EditView, PanelHeader, ReadView,
  Section + transcriptionMarkers, blockConflictMerge, saveBlockWithConflictRetry
  + useBlockAutoSave, useBlockDragDrop hooks
- annotation/: AnnotationLayer, AnnotationShape, AnnotationEditOverlay
- viewer/: PdfViewer, PdfControls + useFileLoader, usePdfRenderer hooks

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

frontend/src/lib/document/viewer/usePdfRenderer.svelte.ts

@@ -0,0 +1,203 @@
+import type { PDFDocumentProxy, RenderTask } from 'pdfjs-dist';
+
+export function createPdfRenderer() {
+	// Reactive state — exposed via getters
+	let currentPage = $state(1);
+	let totalPages = $state(0);
+	let scale = $state(1.5);
+	let loading = $state(false);
+	let error = $state<string | null>(null);
+	let pdfjsReady = $state(false);
+
+	// Internal mutable refs — NOT $state to avoid reactive loops
+	let pdfDoc: PDFDocumentProxy | null = null;
+	let canvasEl: HTMLCanvasElement | null = null;
+	let textLayerEl: HTMLDivElement | null = null;
+	let renderTask: RenderTask | null = null;
+	let textLayerInstance: { cancel: () => void } | null = null;
+	let pdfjsLib: typeof import('pdfjs-dist') | null = null;
+
+	async function init(): Promise<void> {
+		const [lib, { default: workerUrl }] = await Promise.all([
+			import('pdfjs-dist'),
+			import('pdfjs-dist/build/pdf.worker.min.mjs?url')
+		]);
+		lib.GlobalWorkerOptions.workerSrc = workerUrl;
+		pdfjsLib = lib;
+		pdfjsReady = true;
+	}
+
+	function setElements(canvas: HTMLCanvasElement, textLayer: HTMLDivElement): void {
+		canvasEl = canvas;
+		textLayerEl = textLayer;
+	}
+
+	async function loadDocument(src: string): Promise<void> {
+		if (!pdfjsLib) return;
+		loading = true;
+		error = null;
+		pdfDoc = null;
+		currentPage = 1;
+		totalPages = 0;
+
+		try {
+			const loadingTask = pdfjsLib.getDocument(src);
+			const doc = await loadingTask.promise;
+			pdfDoc = doc;
+			totalPages = doc.numPages;
+		} catch (e) {
+			error = e instanceof Error ? e.message : 'Failed to load PDF';
+		} finally {
+			loading = false;
+		}
+	}
+
+	async function renderCurrentPage(): Promise<void> {
+		if (!pdfjsLib || !canvasEl || !textLayerEl || !pdfDoc) return;
+
+		if (renderTask) {
+			renderTask.cancel();
+			renderTask = null;
+		}
+		if (textLayerInstance) {
+			textLayerInstance.cancel();
+			textLayerInstance = null;
+		}
+
+		let page;
+		try {
+			page = await pdfDoc.getPage(currentPage);
+		} catch {
+			return;
+		}
+
+		const dpr = window.devicePixelRatio || 1;
+		const viewport = page.getViewport({ scale: scale * dpr });
+
+		const canvas = canvasEl;
+		const ctx = canvas.getContext('2d');
+		if (!ctx) return;
+
+		canvas.width = viewport.width;
+		canvas.height = viewport.height;
+		canvas.style.width = `${viewport.width / dpr}px`;
+		canvas.style.height = `${viewport.height / dpr}px`;
+
+		const task = page.render({ canvas, canvasContext: ctx, viewport });
+		renderTask = task;
+
+		try {
+			await task.promise;
+		} catch (e: unknown) {
+			if (
+				typeof e === 'object' &&
+				e !== null &&
+				'name' in e &&
+				(e as { name: string }).name === 'RenderingCancelledException'
+			)
+				return;
+			return;
+		}
+		renderTask = null;
+
+		const textDiv = textLayerEl;
+		if (!textDiv) return;
+		textDiv.innerHTML = '';
+		textDiv.style.width = `${viewport.width / dpr}px`;
+		textDiv.style.height = `${viewport.height / dpr}px`;
+
+		const tl = new pdfjsLib.TextLayer({
+			textContentSource: page.streamTextContent(),
+			container: textDiv,
+			viewport
+		});
+		textLayerInstance = tl;
+		try {
+			await tl.render();
+		} catch {
+			// cancelled
+		}
+	}
+
+	async function prerender(): Promise<void> {
+		if (!pdfDoc) return;
+		const neighbors = [currentPage - 1, currentPage + 1].filter(
+			(n) => n >= 1 && n <= (pdfDoc?.numPages ?? 0)
+		);
+		for (const n of neighbors) {
+			try {
+				await pdfDoc.getPage(n);
+			} catch {
+				// ignore
+			}
+		}
+	}
+
+	function prevPage(): void {
+		if (currentPage > 1) currentPage -= 1;
+	}
+
+	function nextPage(): void {
+		if (currentPage < totalPages) currentPage += 1;
+	}
+
+	function goToPage(n: number): void {
+		if (n >= 1 && n <= totalPages) currentPage = n;
+	}
+
+	function zoomIn(): void {
+		scale += 0.25;
+	}
+
+	function zoomOut(): void {
+		if (scale > 0.5) scale -= 0.25;
+	}
+
+	function destroy(): void {
+		if (renderTask) {
+			renderTask.cancel();
+			renderTask = null;
+		}
+		if (textLayerInstance) {
+			textLayerInstance.cancel();
+			textLayerInstance = null;
+		}
+		pdfDoc?.destroy();
+		pdfDoc = null;
+	}
+
+	return {
+		get currentPage() {
+			return currentPage;
+		},
+		get totalPages() {
+			return totalPages;
+		},
+		get scale() {
+			return scale;
+		},
+		get loading() {
+			return loading;
+		},
+		get error() {
+			return error;
+		},
+		get isLoaded() {
+			return totalPages > 0;
+		},
+		get pdfjsReady() {
+			return pdfjsReady;
+		},
+		setElements,
+		init,
+		loadDocument,
+		renderCurrentPage,
+		prerender,
+		prevPage,
+		nextPage,
+		goToPage,
+		zoomIn,
+		zoomOut,
+		destroy
+	};
+}