Add UTF-8 filename decoding for multipart uploads in EquipmentService

- Introduced a new utility function to decode filenames from multipart uploads that may be misencoded as ISO-8859-1.
- Updated EquipmentService to utilize this function when processing file attachments, ensuring correct original file names are stored and returned.

server/src/common/multipart-filename.ts

@@ -0,0 +1,32 @@
+/**
+ * Busboy/Multer often pass multipart `filename` where UTF-8 bytes were read as ISO-8859-1,
+ * which looks like mojibake in the UI (e.g. Cyrillic → "Акт...").
+ * Re-encode the string as Latin-1 bytes and decode as UTF-8.
+ *
+ * Only applied when every character is in U+0000–U+00FF (typical for this bug).
+ */
+export function decodeUtf8FilenameFromMultipart(name: string): string {
+  if (!name || name.length < 2) {
+    return name;
+  }
+  for (let i = 0; i < name.length; i += 1) {
+    if (name.charCodeAt(i) > 0xff) {
+      return name;
+    }
+  }
+  if (!/[\u00a1-\u00ff]{2}/.test(name)) {
+    return name;
+  }
+  try {
+    const decoded = Buffer.from(name, 'latin1').toString('utf8');
+    if (decoded.includes('\uFFFD')) {
+      return name;
+    }
+    if (decoded === name) {
+      return name;
+    }
+    return decoded;
+  } catch {
+    return name;
+  }
+}

server/src/modules/equipment/equipment.service.ts

@@ -8,6 +8,7 @@ import { EquipmentStatus, Prisma } from '@prisma/client';
 import type { Equipment } from '@prisma/client';
 import { Response } from 'express';
 import type { Express } from 'express';
+import { decodeUtf8FilenameFromMultipart } from '../../common/multipart-filename';
 import { setListHeaders } from '../../common/http';
 import { PrismaService } from '../../prisma/prisma.service';
 import type { StoredAttachmentMeta } from '../../storage/storage.service';
@@ -133,10 +134,11 @@ export class EquipmentService {
 
     await this.deleteStoredAttachmentIfAny(item);
 
-    const objectKey = this.storage.buildEquipmentObjectKey(id, file.originalname);
+    const decodedOriginalName = decodeUtf8FilenameFromMultipart(file.originalname);
+    const objectKey = this.storage.buildEquipmentObjectKey(id, decodedOriginalName);
     const meta: StoredAttachmentMeta = {
       objectKey,
-      originalFileName: file.originalname,
+      originalFileName: decodedOriginalName,
       contentType: file.mimetype || 'application/octet-stream',
       sizeBytes: file.size,
     };
@@ -217,7 +219,7 @@ export class EquipmentService {
     }
     return {
       objectKey: raw.objectKey,
-      originalFileName: raw.originalFileName,
+      originalFileName: decodeUtf8FilenameFromMultipart(raw.originalFileName),
       contentType: raw.contentType,
       sizeBytes: raw.sizeBytes,
       downloadUrl,