feat(shared): add fileUploadRequestSchema for the files upload body

shared/src/file/file.schema.ts

@@ -14,6 +14,17 @@ import { z } from 'zod';
 
 const nullableIdField = z.union([z.string(), z.number()]).nullable().optional();
 
+/**
+ * Multipart text fields riding along with the upload — always strings on the
+ * wire (multipart/form-data has no other type), so no numeric coercion here.
+ */
+export const fileUploadRequestSchema = z.object({
+  place_id: z.string().optional(),
+  description: z.string().optional(),
+  reservation_id: z.string().optional(),
+});
+export type FileUploadRequest = z.infer<typeof fileUploadRequestSchema>;
+
 export const fileUpdateRequestSchema = z.object({
   description: z.string().optional(),
   place_id: nullableIdField,