fix: address review feedback — stale error message and * wildcard

- assets.ts: change "Image exceeds" to "File exceeds" in size-limit error
- attachment-types.ts: handle plain "*" as allow-all wildcard pattern
- Add test for "*" wildcard (12 tests total)

server/src/routes/assets.ts

@@ -33,7 +33,7 @@ export function assetRoutes(db: Db, storage: StorageService) {
     } catch (err) {
       if (err instanceof multer.MulterError) {
         if (err.code === "LIMIT_FILE_SIZE") {
-          res.status(422).json({ error: `Image exceeds ${MAX_ATTACHMENT_BYTES} bytes` });
+          res.status(422).json({ error: `File exceeds ${MAX_ATTACHMENT_BYTES} bytes` });
           return;
         }
         res.status(400).json({ error: err.message });