Add issue attachments

- IssueAttachment link table (issue <-> file) + migration
- GET/POST /issues/:issueId/attachments, DELETE .../attachments/:fileId
- Only own uploaded files can be attached; attach is idempotent
- Registers issues as a file owner: attached files stay visible to issue
  participants and are not collected by GC
- IssueDetail.attachments GraphQL field via @ResolveField, issue module untouched

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

prisma/migrations/20261002050156_issue_attachment/migration.sql

@@ -0,0 +1,18 @@
+-- CreateTable
+CREATE TABLE "issue_attachment" (
+    "issueId" INTEGER NOT NULL,
+    "fileId" TEXT NOT NULL,
+    "createdAt" TIMESTAMPTZ(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "issue_attachment_pkey" PRIMARY KEY ("issueId","fileId")
+);
+
+-- CreateIndex
+CREATE INDEX "issue_attachment_fileId_idx" ON "issue_attachment"("fileId");
+
+-- AddForeignKey
+ALTER TABLE "issue_attachment" ADD CONSTRAINT "issue_attachment_issueId_fkey" FOREIGN KEY ("issueId") REFERENCES "issue"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "issue_attachment" ADD CONSTRAINT "issue_attachment_fileId_fkey" FOREIGN KEY ("fileId") REFERENCES "file"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+

prisma/schema.prisma

@@ -81,22 +81,23 @@ model Verification {
 }
 
 model Issue {
-  id         Int       @id @default(autoincrement())
-  key        String
-  title      String
-  content    String?
-  status     String
-  priority   Int       @default(0)
-  assigneeId String?
-  assignee   User?     @relation(name: "assigneeIssues", fields: [assigneeId], references: [id], onDelete: SetNull)
-  reporterId String?
-  reporter   User?     @relation(name: "reporterIssues", fields: [reporterId], references: [id], onDelete: SetNull)
-  projectId  String
-  project    Project   @relation(fields: [projectId], references: [id], onDelete: Cascade)
-  dueDate    DateTime? @db.Timestamptz(3)
-  comments   Comment[]
-  createdAt  DateTime  @default(now()) @db.Timestamptz(3)
-  updatedAt  DateTime  @updatedAt @db.Timestamptz(3)
+  id          Int               @id @default(autoincrement())
+  key         String
+  title       String
+  content     String?
+  status      String
+  priority    Int               @default(0)
+  assigneeId  String?
+  assignee    User?             @relation(name: "assigneeIssues", fields: [assigneeId], references: [id], onDelete: SetNull)
+  reporterId  String?
+  reporter    User?             @relation(name: "reporterIssues", fields: [reporterId], references: [id], onDelete: SetNull)
+  projectId   String
+  project     Project           @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  dueDate     DateTime?         @db.Timestamptz(3)
+  comments    Comment[]
+  attachments IssueAttachment[]
+  createdAt   DateTime          @default(now()) @db.Timestamptz(3)
+  updatedAt   DateTime          @updatedAt @db.Timestamptz(3)
 
   @@index([status])
   @@index([assigneeId])
@@ -225,8 +226,24 @@ model File {
   uploader   User?    @relation(fields: [uploaderId], references: [id], onDelete: SetNull)
   createdAt  DateTime @default(now()) @db.Timestamptz(3)
 
+  issueAttachments IssueAttachment[]
+
   @@unique([storageKey])
   @@index([uploaderId])
   @@index([createdAt])
   @@map("file")
 }
+
+/// Вложение задачи — связь задачи с файлом. Удаление задачи или файла
+/// удаляет связь каскадом; сам файл, оставшийся без связей, удалит GC.
+model IssueAttachment {
+  issueId   Int
+  issue     Issue    @relation(fields: [issueId], references: [id], onDelete: Cascade)
+  fileId    String
+  file      File     @relation(fields: [fileId], references: [id], onDelete: Cascade)
+  createdAt DateTime @default(now()) @db.Timestamptz(3)
+
+  @@id([issueId, fileId])
+  @@index([fileId])
+  @@map("issue_attachment")
+}