feat(#84): implement instance identity model for federation

Implemented the foundation of federation architecture with instance
identity and connection management:

Database Schema:
- Added Instance model for instance identity with keypair generation
- Added FederationConnection model for workspace-scoped connections
- Added FederationConnectionStatus enum (PENDING, ACTIVE, SUSPENDED, DISCONNECTED)

Service Layer:
- FederationService with instance identity management
- RSA 2048-bit keypair generation for signing
- Public identity endpoint (excludes private key)
- Keypair regeneration capability

API Endpoints:
- GET /api/v1/federation/instance - Returns public instance identity
- POST /api/v1/federation/instance/regenerate-keys - Admin keypair regeneration

Tests:
- 11 tests passing (7 service, 4 controller)
- 100% statement coverage, 100% function coverage
- Follows TDD principles (Red-Green-Refactor)

Configuration:
- Added INSTANCE_NAME and INSTANCE_URL environment variables
- Integrated FederationModule into AppModule

Refs #84

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/api/prisma/schema.prisma

@@ -166,6 +166,13 @@ enum JobStepStatus {
   SKIPPED
 }
 
+enum FederationConnectionStatus {
+  PENDING
+  ACTIVE
+  SUSPENDED
+  DISCONNECTED
+}
+
 // ============================================
 // MODELS
 // ============================================
@@ -226,28 +233,29 @@ model Workspace {
   updatedAt DateTime @updatedAt @map("updated_at") @db.Timestamptz
 
   // Relations
-  owner            User                  @relation("WorkspaceOwner", fields: [ownerId], references: [id], onDelete: Cascade)
-  members          WorkspaceMember[]
-  teams            Team[]
-  tasks            Task[]
-  events           Event[]
-  projects         Project[]
-  activityLogs     ActivityLog[]
-  memoryEmbeddings MemoryEmbedding[]
-  domains          Domain[]
-  ideas            Idea[]
-  relationships    Relationship[]
-  agents           Agent[]
-  agentSessions    AgentSession[]
-  agentTasks       AgentTask[]
-  userLayouts      UserLayout[]
-  knowledgeEntries KnowledgeEntry[]
-  knowledgeTags    KnowledgeTag[]
-  cronSchedules    CronSchedule[]
-  personalities    Personality[]
-  llmSettings      WorkspaceLlmSettings?
-  qualityGates     QualityGate[]
-  runnerJobs       RunnerJob[]
+  owner                 User                   @relation("WorkspaceOwner", fields: [ownerId], references: [id], onDelete: Cascade)
+  members               WorkspaceMember[]
+  teams                 Team[]
+  tasks                 Task[]
+  events                Event[]
+  projects              Project[]
+  activityLogs          ActivityLog[]
+  memoryEmbeddings      MemoryEmbedding[]
+  domains               Domain[]
+  ideas                 Idea[]
+  relationships         Relationship[]
+  agents                Agent[]
+  agentSessions         AgentSession[]
+  agentTasks            AgentTask[]
+  userLayouts           UserLayout[]
+  knowledgeEntries      KnowledgeEntry[]
+  knowledgeTags         KnowledgeTag[]
+  cronSchedules         CronSchedule[]
+  personalities         Personality[]
+  llmSettings           WorkspaceLlmSettings?
+  qualityGates          QualityGate[]
+  runnerJobs            RunnerJob[]
+  federationConnections FederationConnection[]
 
   @@index([ownerId])
   @@map("workspaces")
@@ -1217,3 +1225,58 @@ model JobEvent {
   @@index([jobId, timestamp])
   @@map("job_events")
 }
+
+// ============================================
+// FEDERATION MODULE
+// ============================================
+
+model Instance {
+  id         String @id @default(uuid()) @db.Uuid
+  instanceId String @unique @map("instance_id") // Unique identifier for federation
+  name       String
+  url        String
+  publicKey  String @map("public_key") @db.Text
+  privateKey String @map("private_key") @db.Text // Encrypted private key
+
+  // Capabilities and metadata
+  capabilities Json @default("{}")
+  metadata     Json @default("{}")
+
+  // Timestamps
+  createdAt DateTime @default(now()) @map("created_at") @db.Timestamptz
+  updatedAt DateTime @updatedAt @map("updated_at") @db.Timestamptz
+
+  @@map("instances")
+}
+
+model FederationConnection {
+  id          String @id @default(uuid()) @db.Uuid
+  workspaceId String @map("workspace_id") @db.Uuid
+
+  // Remote instance details
+  remoteInstanceId   String @map("remote_instance_id")
+  remoteUrl          String @map("remote_url")
+  remotePublicKey    String @map("remote_public_key") @db.Text
+  remoteCapabilities Json   @default("{}") @map("remote_capabilities")
+
+  // Connection status
+  status FederationConnectionStatus @default(PENDING)
+
+  // Metadata
+  metadata Json @default("{}")
+
+  // Timestamps
+  createdAt      DateTime  @default(now()) @map("created_at") @db.Timestamptz
+  updatedAt      DateTime  @updatedAt @map("updated_at") @db.Timestamptz
+  connectedAt    DateTime? @map("connected_at") @db.Timestamptz
+  disconnectedAt DateTime? @map("disconnected_at") @db.Timestamptz
+
+  // Relations
+  workspace Workspace @relation(fields: [workspaceId], references: [id], onDelete: Cascade)
+
+  @@unique([workspaceId, remoteInstanceId])
+  @@index([workspaceId])
+  @@index([workspaceId, status])
+  @@index([remoteInstanceId])
+  @@map("federation_connections")
+}