feat(03-01): add storage and thumbnail utilities

- Add storage.ts with directory management and file I/O
- Add thumbnails.ts with EXIF-aware thumbnail generation
- Thumbnails always output as JPEG with 80% quality

src/lib/server/images/thumbnails.ts

@@ -0,0 +1,23 @@
+import sharp from 'sharp';
+
+/**
+ * Generate a thumbnail from an image buffer
+ *
+ * CRITICAL: Uses sharp.rotate() first to handle EXIF orientation from mobile photos.
+ * Without this, photos taken in portrait mode may appear rotated.
+ *
+ * @param buffer - Original image buffer
+ * @param size - Thumbnail size (default 150px)
+ * @returns Thumbnail buffer as JPEG
+ */
+export async function generateThumbnail(buffer: Buffer, size: number = 150): Promise<Buffer> {
+	return sharp(buffer)
+		.rotate() // Auto-rotate based on EXIF orientation
+		.resize(size, size, {
+			fit: 'cover',
+			position: 'center',
+			withoutEnlargement: true
+		})
+		.jpeg({ quality: 80 })
+		.toBuffer();
+}