Add multer upload config (image-only, size-limited, safe names)

server/upload.js

@@ -0,0 +1,27 @@
+import multer from "multer";
+import path from "path";
+import crypto from "crypto";
+import { fileURLToPath } from "url";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+export const UPLOAD_DIR = path.join(__dirname, "uploads");
+
+const ALLOWED = new Set(["image/gif", "image/png", "image/webp"]);
+
+const storage = multer.diskStorage({
+  destination: (_req, _file, cb) => cb(null, UPLOAD_DIR),
+  filename: (_req, file, cb) => {
+    const ext = path.extname(file.originalname).toLowerCase().replace(/[^.a-z0-9]/g, "");
+    const safeExt = [".gif", ".png", ".webp"].includes(ext) ? ext : ".gif";
+    cb(null, crypto.randomUUID() + safeExt);
+  },
+});
+
+export const upload = multer({
+  storage,
+  limits: { fileSize: 8 * 1024 * 1024 }, // 8 MB
+  fileFilter: (_req, file, cb) => {
+    if (ALLOWED.has(file.mimetype)) cb(null, true);
+    else cb(new Error("Only GIF, PNG, or WebP images are allowed"));
+  },
+});