improvement: attachment selection for lab dispatch added. attachment preview added to cases feature.

backend/prisma/schema.prisma

@@ -179,6 +179,7 @@ model TreatmentDetailAttachment {
   storagePath     String
 
   detail TreatmentDetail? @relation(fields: [detailId], references: [id], onDelete: Cascade)
+  labCaseLinks LabCaseAttachment[]
 
   createdAt DateTime @default(now())
 
@@ -201,11 +202,24 @@ model LabCase {
   tasks           LabCaseTask[]
   toothProsthesis LabCaseToothProsthesis[]
   comments        LabCaseComment[]
+  attachments     LabCaseAttachment[]
 
   @@index([treatmentId, sortOrder])
   @@map("lab_cases")
 }
 
+model LabCaseAttachment {
+  labCaseId    String
+  attachmentId String
+
+  labCase    LabCase                   @relation(fields: [labCaseId], references: [id], onDelete: Cascade)
+  attachment TreatmentDetailAttachment @relation(fields: [attachmentId], references: [id], onDelete: Cascade)
+
+  @@id([labCaseId, attachmentId])
+  @@index([attachmentId])
+  @@map("lab_case_attachments")
+}
+
 model LabCaseDetail {
   labCaseId         String
   treatmentDetailId String @unique