feat(api): add terminal session persistence with Prisma model and CRUD service

Adds database-backed TerminalSession model with ACTIVE/CLOSED status enum,
migration SQL, TerminalSessionService (create/findByWorkspace/close/findById),
DTO file with class-validator decorators, unit tests (12 tests), and module
registration. Workspace relation and indexed columns enable efficient session
listing and recovery.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/prisma/schema.prisma

@@ -206,6 +206,11 @@ enum CredentialScope {
   SYSTEM
 }
 
+enum TerminalSessionStatus {
+  ACTIVE
+  CLOSED
+}
+
 // ============================================
 // MODELS
 // ============================================
@@ -297,6 +302,7 @@ model Workspace {
   federationEventSubscriptions FederationEventSubscription[]
   llmUsageLogs                 LlmUsageLog[]
   userCredentials              UserCredential[]
+  terminalSessions             TerminalSession[]
 
   @@index([ownerId])
   @@map("workspaces")
@@ -1507,3 +1513,23 @@ model LlmUsageLog {
   @@index([conversationId])
   @@map("llm_usage_logs")
 }
+
+// ============================================
+// TERMINAL MODULE
+// ============================================
+
+model TerminalSession {
+  id          String                @id @default(uuid()) @db.Uuid
+  workspaceId String                @map("workspace_id") @db.Uuid
+  name        String                @default("Terminal")
+  status      TerminalSessionStatus @default(ACTIVE)
+  createdAt   DateTime              @default(now()) @map("created_at") @db.Timestamptz
+  closedAt    DateTime?             @map("closed_at") @db.Timestamptz
+
+  // Relations
+  workspace Workspace @relation(fields: [workspaceId], references: [id], onDelete: Cascade)
+
+  @@index([workspaceId])
+  @@index([workspaceId, status])
+  @@map("terminal_sessions")
+}