feat: add pipeline API and download utilities

- processImageWithPipeline for full pipeline processing
- ZIP archive creation with JSZip
- File download helpers
- Output filename generation

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

src/lib/processing/pipeline.ts

@@ -0,0 +1,102 @@
+// High-level pipeline API for image processing
+
+import type { Device, ImageEntry, PipelineConfig } from '$lib/types';
+import { getExtension } from '$lib/types';
+import JSZip from 'jszip';
+import { initPhoton } from './photon';
+import { workerPool } from './workerPool';
+
+let photonReady = false;
+
+export async function ensurePhotonReady(): Promise<void> {
+	if (photonReady) return;
+	await initPhoton();
+	photonReady = true;
+}
+
+export async function processImage(file: File, device: Device): Promise<Blob> {
+	const { blob } = await processImageWithPipeline(file, device, {
+		crop: { enabled: true, mode: 'center' },
+		resize: { enabled: true, mode: 'cover' },
+		brightness: { enabled: false, value: 0 },
+		contrast: { enabled: false, value: 0 },
+		gamma: { enabled: false, value: 1.0 },
+		autoLevels: { enabled: false, clipPercent: 0.5 },
+		greyscale: { enabled: true, method: 'luminosity' },
+		sharpen: { enabled: false, amount: 0 },
+		quantize: { enabled: true, levels: device.greyLevels },
+		dither: { enabled: false, algorithm: 'floyd-steinberg' }
+	});
+	return blob;
+}
+
+export async function processImageWithPreview(
+	file: File,
+	device: Device
+): Promise<{ blob: Blob; dataUrl: string }> {
+	return processImageWithPipeline(file, device, {
+		crop: { enabled: true, mode: 'center' },
+		resize: { enabled: true, mode: 'cover' },
+		brightness: { enabled: false, value: 0 },
+		contrast: { enabled: false, value: 0 },
+		gamma: { enabled: false, value: 1.0 },
+		autoLevels: { enabled: false, clipPercent: 0.5 },
+		greyscale: { enabled: true, method: 'luminosity' },
+		sharpen: { enabled: false, amount: 0 },
+		quantize: { enabled: true, levels: device.greyLevels },
+		dither: { enabled: false, algorithm: 'floyd-steinberg' }
+	});
+}
+
+export async function processImageWithPipeline(
+	file: File,
+	device: Device,
+	config: PipelineConfig
+): Promise<{ blob: Blob; dataUrl: string }> {
+	return workerPool.process(file, device, config);
+}
+
+export function getOutputFilename(originalFilename: string, device: Device): string {
+	const lastDot = originalFilename.lastIndexOf('.');
+	const stem = lastDot > 0 ? originalFilename.substring(0, lastDot) : originalFilename;
+	const ext = getExtension(device.outputFormat);
+	return `${stem}_${device.id}.${ext}`;
+}
+
+export async function createZipArchive(images: ImageEntry[], device: Device): Promise<Blob> {
+	const zip = new JSZip();
+
+	for (const image of images) {
+		if (image.processedBlob) {
+			const filename = getOutputFilename(image.filename, device);
+			zip.file(filename, image.processedBlob);
+		}
+	}
+
+	return zip.generateAsync({ type: 'blob' });
+}
+
+export function downloadFile(blob: Blob, filename: string): void {
+	const url = URL.createObjectURL(blob);
+	const a = document.createElement('a');
+	a.href = url;
+	a.download = filename;
+	document.body.appendChild(a);
+	a.click();
+	document.body.removeChild(a);
+	URL.revokeObjectURL(url);
+}
+
+export function downloadImage(image: ImageEntry, device: Device): void {
+	if (!image.processedBlob) return;
+	const filename = getOutputFilename(image.filename, device);
+	downloadFile(image.processedBlob, filename);
+}
+
+export async function downloadAllAsZip(images: ImageEntry[], device: Device): Promise<void> {
+	const completedImages = images.filter((img) => img.status === 'complete' && img.processedBlob);
+	if (completedImages.length === 0) return;
+
+	const zipBlob = await createZipArchive(completedImages, device);
+	downloadFile(zipBlob, '2eink_covers.zip');
+}