feat: document file conversion

packages/prisma/migrations/20251210213745_add_original_mime_type_to_document_data/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "DocumentData" ADD COLUMN     "originalMimeType" TEXT;

packages/prisma/schema.prisma

@@ -486,11 +486,12 @@ enum DocumentSigningOrder {
 }
 
 model DocumentData {
-  id           String           @id @default(cuid())
-  type         DocumentDataType
-  data         String
-  initialData  String
-  envelopeItem EnvelopeItem?
+  id               String           @id @default(cuid())
+  type             DocumentDataType
+  data             String
+  initialData      String
+  originalMimeType String?
+  envelopeItem     EnvelopeItem?
 }
 
 enum DocumentDistributionMethod {