feat(ai): image-preprocess mit sharp (Resize + JPEG + EXIF-Strip)

src/lib/server/ai/image-preprocess.ts

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+import sharp from 'sharp';
+
+const MAX_EDGE = 1600;
+const JPEG_QUALITY = 85;
+
+export type PreprocessedImage = {
+  buffer: Buffer;
+  mimeType: 'image/jpeg';
+};
+
+// Resize auf max 1600px lange Kante, JPEG re-encode, Metadata strippen.
+// sharp liest HEIC/HEIF transparent, wenn libheif im libvips-Build enthalten ist
+// (in Alpine's vips-dev + in den offiziellen sharp-Prebuilds).
+export async function preprocessImage(input: Buffer): Promise<PreprocessedImage> {
+  const pipeline = sharp(input, { failOn: 'error' }).rotate(); // respect EXIF orientation
+  const meta = await pipeline.metadata();
+  if (!meta.width || !meta.height) {
+    throw new Error('Unable to read image dimensions');
+  }
+
+  const longEdge = Math.max(meta.width, meta.height);
+  const resized =
+    longEdge > MAX_EDGE
+      ? pipeline.resize({
+          width: meta.width >= meta.height ? MAX_EDGE : undefined,
+          height: meta.height > meta.width ? MAX_EDGE : undefined,
+          withoutEnlargement: true
+        })
+      : pipeline;
+
+  // Default-Verhalten seit sharp 0.33: alle Metadata (EXIF/IPTC/XMP) werden
+  // gestripped. Nur `.keepMetadata()`/`.keepExif()` würde sie erhalten.
+  const buffer = await resized
+    .jpeg({ quality: JPEG_QUALITY, mozjpeg: true })
+    .toBuffer();
+
+  return { buffer, mimeType: 'image/jpeg' };
+}